def setUp(self):
x = np.linspace(0, np.pi, 5)
self.d2 = PlotData(np.sin(x),
x,
xlab='x',
ylab='sin',
title='sinus',
plot_args=['r.'])
self.x = x
def edf(x, method=2):
"""
Returns Empirical Distribution Function (EDF).
Parameters
----------
x : array-like
data vector
method : integer scalar
1. Interpolation so that F(X_(k)) == (k-0.5)/n.
2. Interpolation so that F(X_(k)) == k/(n+1). (default)
3. The empirical distribution. F(X_(k)) = k/n
Examples
--------
>>> import wafo.stats as ws
>>> x = np.linspace(0,6,200)
>>> R = ws.rayleigh.rvs(scale=2,size=100)
>>> F = ws.edf(R)
>>> h = F.plot()
See also edf, pdfplot, cumtrapz
"""
z = atleast_1d(x)
z.sort()
n = len(z)
if method == 1:
e_cdf = arange(0.5, n) / n
elif method == 3:
e_cdf = arange(1, n + 1) / n
else:
e_cdf = arange(1, n + 1) / (n + 1)
return PlotData(e_cdf, z, xlab='x', ylab='F(x)', plotmethod='step')
def prb_search_best(self, prb_e=None, hsvec=None, hsfun='hste',
alpha=0.05, color='r', label=''):
"""Return best smoothed binomial probability.
Parameters
----------
prb_e : PlotData object with empirical binomial probabilites
hsvec : arraylike (default np.linspace(hsmax*0.1,hsmax,55))
vector smoothing parameters
hsfun :
method for calculating hsmax
"""
if prb_e is None:
prb_e = self.prb_empirical(alpha=alpha, color=color)
if hsvec is None:
hsmax = max(self._get_max_smoothing(hsfun)[0], self.hs_e)
hsvec = np.linspace(hsmax * 0.2, hsmax, 55)
hs_best = hsvec[-1] + 0.1
prb_best = self.prb_smoothed(prb_e, hs_best, alpha, color, label)
aicc = np.zeros(np.size(hsvec))
for i, hi in enumerate(hsvec):
f = self.prb_smoothed(prb_e, hi, alpha, color, label)
aicc[i] = f.aicc
if f.aicc <= prb_best.aicc:
prb_best = f
hs_best = hi
prb_best.score = PlotData(aicc, hsvec)
prb_best.hs = hs_best
self._set_smoothing(hs_best)
return prb_best
def __init__(self, *args, **kwds):
options = dict(
title='Transform',
xlab='x',
ylab='g(x)',
plot_args=['r'],
plot_args_children=['g--'],
)
options.update(**kwds)
super(TrData, self).__init__(*args, **options)
self.ymean = kwds.get('ymean', 0e0)
self.ysigma = kwds.get('ysigma', 1e0)
self.mean = kwds.get('mean')
self.sigma = kwds.get('sigma')
if self.mean is None:
# self.mean = np.mean(self.args)
self.mean = self.gauss2dat(self.ymean)
if self.sigma is None:
yp = self.ymean + self.ysigma
ym = self.ymean - self.ysigma
self.sigma = (self.gauss2dat(yp) - self.gauss2dat(ym)) / 2.
self.children = [
PlotData((self.args - self.mean) / self.sigma, self.args)
]
def prb_smoothed(self, prb_e, hs, alpha=0.05, color='r', label=''):
"""Return smoothed binomial probability.
Parameters
----------
prb_e : PlotData object with empirical binomial probabilites
hs : smoothing parameter
alpha : confidence level
color : color of plot object
label : label for plot object
"""
x_e = prb_e.args
n_e = len(x_e)
dx_e = x_e[1] - x_e[0]
n = self.x.size
x_s = np.linspace(x_e[0], x_e[-1], 10 * n_e + 1)
self.hs = hs
prb_s = self.kreg(x_s, output='plotobj', title='', plot_kwds=dict(
color=color, linewidth=2)) # dict(plotflag=7))
m_nan = np.isnan(prb_s.data)
if m_nan.any(): # assume 0/0 division
prb_s.data[m_nan] = 0.0
# prb_s.data[np.isnan(prb_s.data)] = 0
# expected number of data in each bin
c_s = self.kreg.tkde.eval_grid_fast(x_s) * dx_e * n
plo, pup = self.prb_ci(c_s, prb_s.data, alpha)
prb_s.dataCI = np.vstack((plo, pup)).T
prb_s.prediction_error_avg = (np.trapz(pup - plo, x_s) /
(x_s[-1] - x_s[0]))
if label:
prb_s.plot_kwds['label'] = label
prb_s.children = [PlotData([plo, pup], x_s,
plotmethod='fill_between',
plot_kwds=dict(alpha=0.2, color=color)),
prb_e]
p_e = prb_e.eval_points(x_s)
p_s = prb_s.data
dp_s = np.sign(np.diff(p_s))
k = (dp_s[:-1] != dp_s[1:]).sum() # numpeaks
sigmai = _logit(pup) - _logit(plo) + _EPS
aicc = ((((_logit(p_e) - _logit(p_s)) / sigmai) ** 2).sum() +
2 * k * (k + 1) / np.maximum(n_e - k + 1, 1) +
np.abs((p_e - pup).clip(min=0) -
(p_e - plo).clip(max=0)).sum())
prb_s.aicc = aicc
return prb_s
def prb_empirical(self, xi=None, hs_e=None, alpha=0.05, color='r', **kwds):
"""Returns empirical binomial probabiltity.
Parameters
----------
x : ndarray
position vector
y : ndarray
binomial response variable (zeros and ones)
alpha : scalar
confidence level
color:
used in plot
Returns
-------
P(x) : PlotData object
empirical probability
"""
if xi is None:
xi = self.get_grid(hs_e)
x = self.x
y = self.y
c = gridcount(x, xi) # + self.a + self.b # count data
if np.any(y == 1):
c0 = gridcount(x[y == 1], xi) # + self.a # count success
else:
c0 = np.zeros(np.shape(xi))
prb = np.where(c == 0, 0, c0 / (c + _TINY)) # assume prb==0 for c==0
CI = np.vstack(self.prb_ci(c, prb, alpha))
prb_e = PlotData(prb,
xi,
plotmethod='plot',
plot_args=['.'],
plot_kwds=dict(markersize=6, color=color, picker=5))
prb_e.dataCI = CI.T
prb_e.count = c
return prb_e
def _make_object(self, f, **kwds):
titlestr = 'Kernel density estimate ({})'.format(self.kernel.name)
kwds2 = dict(title=titlestr)
kwds2['plot_kwds'] = dict(plotflag=1)
kwds2.update(**kwds)
args = self.args
if self.d == 1:
args = args[0]
wdata = PlotData(f, args, **kwds2)
if self.d > 1:
self._add_contour_levels(wdata)
return wdata
def edf(x, method=2):
'''
Returns Empirical Distribution Function (EDF).
Parameters
----------
x : array-like
data vector
method : integer scalar
1. Interpolation so that F(X_(k)) == (k-0.5)/n.
2. Interpolation so that F(X_(k)) == k/(n+1). (default)
3. The empirical distribution. F(X_(k)) = k/n
Example
-------
>>> import wafo.stats as ws
>>> x = np.linspace(0,6,200)
>>> R = ws.rayleigh.rvs(scale=2,size=100)
>>> F = ws.edf(R)
>>> h = F.plot()
See also edf, pdfplot, cumtrapz
'''
z = atleast_1d(x)
z.sort()
N = len(z)
if method == 1:
Fz1 = arange(0.5, N) / N
elif method == 3:
Fz1 = arange(1, N + 1) / N
else:
Fz1 = arange(1, N + 1) / (N + 1)
F = PlotData(Fz1, z, xlab='x', ylab='F(x)')
F.setplotter('step')
return F
def edf(x, method=2):
'''
Returns Empirical Distribution Function (EDF).
Parameters
----------
x : array-like
data vector
method : integer scalar
1. Interpolation so that F(X_(k)) == (k-0.5)/n.
2. Interpolation so that F(X_(k)) == k/(n+1). (default)
3. The empirical distribution. F(X_(k)) = k/n
Example
-------
>>> import wafo.stats as ws
>>> x = np.linspace(0,6,200)
>>> R = ws.rayleigh.rvs(scale=2,size=100)
>>> F = ws.edf(R)
>>> h = F.plot()
See also edf, pdfplot, cumtrapz
'''
z = atleast_1d(x)
z.sort()
N = len(z)
if method == 1:
Fz1 = arange(0.5, N) / N
elif method == 3:
Fz1 = arange(1, N + 1) / N
else:
Fz1 = arange(1, N + 1) / (N + 1)
F = PlotData(Fz1, z, xlab='x', ylab='F(x)')
F.setplotter('step')
return F
class TestPlotData(unittest.TestCase):
def setUp(self):
x = np.linspace(0, np.pi, 5)
self.d2 = PlotData(np.sin(x), x,
xlab='x', ylab='sin', title='sinus',
plot_args=['r.'])
self.x = x
def tearDown(self):
pass
def test_copy(self):
d3 = self.d2.copy() # shallow copy
self.d2.args = None
assert_array_almost_equal(d3.args, self.x)
def test_labels_str(self):
txt = str(self.d2.labels)
self.assertEqual(txt,
'AxisLabels(title=sinus, xlab=x, ylab=sin, zlab=)')
class TestPlotData(unittest.TestCase):
def setUp(self):
x = np.linspace(0, np.pi, 5)
self.d2 = PlotData(np.sin(x),
x,
xlab='x',
ylab='sin',
title='sinus',
plot_args=['r.'])
self.x = x
def tearDown(self):
pass
def test_copy(self):
d3 = self.d2.copy() # shallow copy
self.d2.args = None
assert_array_almost_equal(d3.args, self.x)
def test_labels_str(self):
txt = str(self.d2.labels)
self.assertEqual(txt,
'AxisLabels(title=sinus, xlab=x, ylab=sin, zlab=)')
def tocovdata(self, timeseries):
"""
Return auto covariance function from data.
Return
-------
acf : CovData1D object
with attributes:
data : ACF vector length L+1
args : time lags length L+1
sigma : estimated large lag standard deviation of the estimate
assuming x is a Gaussian process:
if acf[k]=0 for all lags k>q then an approximation
of the variance for large samples due to Bartlett
var(acf[k])=1/N*(acf[0]**2+2*acf[1]**2+2*acf[2]**2+ ..+2*acf[q]**2)
for k>q and where N=length(x). Special case is
white noise where it equals acf[0]**2/N for k>0
norm : bool
If false indicating that auto_cov is not normalized
Example:
--------
>>> import wafo.data
>>> import wafo.objects as wo
>>> x = wafo.data.sea()
>>> ts = wo.mat2timeseries(x)
>>> acf = ts.tocovdata(150)
h = acf.plot()
"""
lag = self.lag
window = self.window
detrend = self.detrend
try:
x = timeseries.data.flatten('F')
dt = timeseries.sampling_period()
except Exception:
x = timeseries[:, 1:].flatten('F')
dt = sampling_period(timeseries[:, 0])
if self.dt is not None:
dt = self.dt
if self.tr is not None:
x = self.tr.dat2gauss(x)
n = len(x)
indnan = np.isnan(x)
if any(indnan):
x = x - x[1 - indnan].mean()
Ncens = n - indnan.sum()
x[indnan] = 0.
else:
Ncens = n
x = x - x.mean()
if hasattr(detrend, '__call__'):
x = detrend(x)
nfft = 2 ** nextpow2(n)
raw_periodogram = abs(fft(x, nfft)) ** 2 / Ncens
# ifft = fft/nfft since raw_periodogram is real!
auto_cov = np.real(fft(raw_periodogram)) / nfft
if self.flag.startswith('unbiased'):
# unbiased result, i.e. divide by n-abs(lag)
auto_cov = auto_cov[:Ncens] * Ncens / np.arange(Ncens, 1, -1)
if self.norm:
auto_cov = auto_cov / auto_cov[0]
if lag is None:
lag = self._estimate_lag(auto_cov, Ncens)
lag = min(lag, n - 2)
if isinstance(window, str) or type(window) is tuple:
win = get_window(window, 2 * lag - 1)
else:
win = np.asarray(window)
auto_cov[:lag] = auto_cov[:lag] * win[lag - 1::]
auto_cov[lag] = 0
lags = slice(0, lag + 1)
t = np.linspace(0, lag * dt, lag + 1)
acf = CovData1D(auto_cov[lags], t)
acf.sigma = np.sqrt(np.r_[0, auto_cov[0] ** 2,
auto_cov[0] ** 2 + 2 * np.cumsum(auto_cov[1:] ** 2)] / Ncens)
acf.children = [PlotData(-2. * acf.sigma[lags], t),
PlotData(2. * acf.sigma[lags], t)]
acf.plot_args_children = ['r:']
acf.norm = self.norm
return acf
def dispersion_idx(
data, t=None, u=None, umin=None, umax=None, nu=None, nmin=10, tb=1,
alpha=0.05, plotflag=False):
'''Return Dispersion Index vs threshold
Parameters
----------
data, ti : array_like
data values and sampled times, respectively.
u : array-like
threshold values (default linspace(umin, umax, nu))
umin, umax : real scalars
Minimum and maximum threshold, respectively
(default min(data), max(data)).
nu : scalar integer
number of threshold values (default min(N-nmin,100))
nmin : scalar integer
Minimum number of extremes to include. (Default 10).
tb : Real scalar
Block period (same unit as the sampled times) (default 1)
alpha : real scalar
Confidence coefficient (default 0.05)
plotflag: bool
Returns
-------
DI : PlotData object
Dispersion index
b_u : real scalar
threshold where the number of exceedances in a fixed period (Tb) is
consistent with a Poisson process.
ok_u : array-like
all thresholds where the number of exceedances in a fixed period (Tb)
is consistent with a Poisson process.
Notes
------
DISPRSNIDX estimate the Dispersion Index (DI) as function of threshold.
DI measures the homogenity of data and the purpose of DI is to determine
the threshold where the number of exceedances in a fixed period (Tb) is
consistent with a Poisson process. For a Poisson process the DI is one.
Thus the threshold should be so high that DI is not significantly
different from 1.
The Poisson hypothesis is not rejected if the estimated DI is between:
chi2(alpha/2, M-1)/(M-1)< DI < chi^2(1 - alpha/2, M-1 }/(M - 1)
where M is the total number of fixed periods/blocks -generally
the total number of years in the sample.
Example
-------
>>> import wafo.data
>>> xn = wafo.data.sea()
>>> t, data = xn.T
>>> Ie = findpot(data,t,0,5);
>>> di, u, ok_u = dispersion_idx(data[Ie],t[Ie],tb=100)
>>> h = di.plot() # a threshold around 1 seems appropriate.
>>> round(u*100)/100
1.03
vline(u)
See also
--------
reslife,
fitgenparrange,
extremal_idx
References
----------
Ribatet, M. A.,(2006),
A User's Guide to the POT Package (Version 1.0)
month = {August},
url = {http://cran.r-project.org/}
Cunnane, C. (1979) Note on the poisson assumption in
partial duration series model. Water Resource Research, 15\bold{(2)}
:489--494.}
'''
n = len(data)
if t is None:
ti = arange(n)
else:
ti = arr(t) - min(t)
t1 = np.empty(ti.shape, dtype=int)
t1[:] = np.floor(ti / tb)
if u is None:
sd = np.sort(data)
nmin = max(nmin, 0)
if 2 * nmin > n:
warnings.warn('nmin possibly too large!')
sdmax, sdmin = sd[-nmin], sd[0]
umax = sdmax if umax is None else min(umax, sdmax)
umin = sdmin if umin is None else max(umin, sdmin)
if nu is None:
nu = min(n - nmin, 100)
u = linspace(umin, umax, nu)
nu = len(u)
di = np.zeros(nu)
d = arr(data)
mint = int(min(t1)) # ; % mint should be 0.
maxt = int(max(t1))
M = maxt - mint + 1
occ = np.zeros(M)
for ix, tresh in enumerate(u.tolist()):
excess = (d > tresh)
lambda_ = excess.sum() / M
for block in range(M):
occ[block] = sum(excess[t1 == block])
di[ix] = occ.var() / lambda_
p = 1 - alpha
diLo = _invchi2(1 - alpha / 2, M - 1) / (M - 1)
diUp = _invchi2(alpha / 2, M - 1) / (M - 1)
# Find appropriate threshold
k1, = np.where((diLo < di) & (di < diUp))
if len(k1) > 0:
ok_u = u[k1]
b_di = (di[k1].mean() < di[k1])
k = b_di.argmax()
b_u = ok_u[k]
else:
b_u = ok_u = None
CItxt = '%d%s CI' % (100 * p, '%')
titleTxt = 'Dispersion Index plot'
res = PlotData(di, u, title=titleTxt,
labx='Threshold', laby='Dispersion Index')
#'caption',CItxt);
res.workspace = dict(umin=umin, umax=umax, nu=nu, nmin=nmin, alpha=alpha)
res.children = [
PlotData(vstack([diLo * ones(nu), diUp * ones(nu)]).T, u,
xlab='Threshold', title=CItxt)]
res.plot_args_children = ['--r']
if plotflag:
res.plot(di)
return res, b_u, ok_u
def reslife(data,
u=None,
umin=None,
umax=None,
nu=None,
nmin=3,
alpha=0.05,
plotflag=False):
'''
Return Mean Residual Life, i.e., mean excesses vs thresholds
Parameters
---------
data : array_like
vector of data of length N.
u : array-like
threshold values (default linspace(umin, umax, nu))
umin, umax : real scalars
Minimum and maximum threshold, respectively
(default min(data), max(data)).
nu : scalar integer
number of threshold values (default min(N-nmin,100))
nmin : scalar integer
Minimum number of extremes to include. (Default 3).
alpha : real scalar
Confidence coefficient (default 0.05)
plotflag: bool
Returns
-------
mrl : PlotData object
Mean residual life values, i.e., mean excesses over thresholds, u.
Notes
-----
RESLIFE estimate mean excesses over thresholds. The purpose of MRL is
to determine the threshold where the upper tail of the data can be
approximated with the generalized Pareto distribution (GPD). The GPD is
appropriate for the tail, if the MRL is a linear function of the
threshold, u. Theoretically in the GPD model
E(X-u0|X>u0) = s0/(1+k)
E(X-u |X>u) = s/(1+k) = (s0 -k*u)/(1+k) for u>u0
where k,s is the shape and scale parameter, respectively.
s0 = scale parameter for threshold u0<u.
Example
-------
>>> import wafo
>>> R = wafo.stats.genpareto.rvs(0.1,2,2,size=100)
>>> mrl = reslife(R,nu=20)
>>> h = mrl.plot()
See also
---------
genpareto
fitgenparrange, disprsnidx
'''
if u is None:
sd = np.sort(data)
n = len(data)
nmin = max(nmin, 0)
if 2 * nmin > n:
warnings.warn('nmin possibly too large!')
sdmax, sdmin = sd[-nmin], sd[0]
umax = sdmax if umax is None else min(umax, sdmax)
umin = sdmin if umin is None else max(umin, sdmin)
if nu is None:
nu = min(n - nmin, 100)
u = linspace(umin, umax, nu)
nu = len(u)
#mrl1 = valarray(nu)
#srl = valarray(nu)
#num = valarray(nu)
mean_and_std = lambda data1: (data1.mean(), data1.std(), data1.size)
dat = arr(data)
tmp = arr([mean_and_std(dat[dat > tresh] - tresh) for tresh in u.tolist()])
mrl, srl, num = tmp.T
p = 1 - alpha
alpha2 = alpha / 2
# Approximate P% confidence interval
#%Za = -invnorm(alpha2); % known mean
Za = -_invt(alpha2, num - 1) # unknown mean
mrlu = mrl + Za * srl / sqrt(num)
mrll = mrl - Za * srl / sqrt(num)
#options.CI = [mrll,mrlu];
#options.numdata = num;
titleTxt = 'Mean residual life with %d%s CI' % (100 * p, '%')
res = PlotData(mrl,
u,
xlab='Threshold',
ylab='Mean Excess',
title=titleTxt)
res.workspace = dict(numdata=num,
umin=umin,
umax=umax,
nu=nu,
nmin=nmin,
alpha=alpha)
res.children = [
PlotData(vstack([mrll, mrlu]).T, u, xlab='Threshold', title=titleTxt)
]
res.plot_args_children = [':r']
if plotflag:
res.plot()
return res
def reslife(data, u=None, umin=None, umax=None, nu=None, nmin=3, alpha=0.05,
plotflag=False):
'''
Return Mean Residual Life, i.e., mean excesses vs thresholds
Parameters
---------
data : array_like
vector of data of length N.
u : array-like
threshold values (default linspace(umin, umax, nu))
umin, umax : real scalars
Minimum and maximum threshold, respectively
(default min(data), max(data)).
nu : scalar integer
number of threshold values (default min(N-nmin,100))
nmin : scalar integer
Minimum number of extremes to include. (Default 3).
alpha : real scalar
Confidence coefficient (default 0.05)
plotflag: bool
Returns
-------
mrl : PlotData object
Mean residual life values, i.e., mean excesses over thresholds, u.
Notes
-----
RESLIFE estimate mean excesses over thresholds. The purpose of MRL is
to determine the threshold where the upper tail of the data can be
approximated with the generalized Pareto distribution (GPD). The GPD is
appropriate for the tail, if the MRL is a linear function of the
threshold, u. Theoretically in the GPD model
E(X-u0|X>u0) = s0/(1+k)
E(X-u |X>u) = s/(1+k) = (s0 -k*u)/(1+k) for u>u0
where k,s is the shape and scale parameter, respectively.
s0 = scale parameter for threshold u0<u.
Example
-------
>>> import wafo
>>> R = wafo.stats.genpareto.rvs(0.1,2,2,size=100)
>>> mrl = reslife(R,nu=20)
>>> h = mrl.plot()
See also
---------
genpareto
fitgenparrange, disprsnidx
'''
if u is None:
sd = np.sort(data)
n = len(data)
nmin = max(nmin, 0)
if 2 * nmin > n:
warnings.warn('nmin possibly too large!')
sdmax, sdmin = sd[-nmin], sd[0]
umax = sdmax if umax is None else min(umax, sdmax)
umin = sdmin if umin is None else max(umin, sdmin)
if nu is None:
nu = min(n - nmin, 100)
u = linspace(umin, umax, nu)
nu = len(u)
#mrl1 = valarray(nu)
#srl = valarray(nu)
#num = valarray(nu)
mean_and_std = lambda data1: (data1.mean(), data1.std(), data1.size)
dat = arr(data)
tmp = arr([mean_and_std(dat[dat > tresh] - tresh) for tresh in u.tolist()])
mrl, srl, num = tmp.T
p = 1 - alpha
alpha2 = alpha / 2
# Approximate P% confidence interval
#%Za = -invnorm(alpha2); % known mean
Za = -_invt(alpha2, num - 1) # unknown mean
mrlu = mrl + Za * srl / sqrt(num)
mrll = mrl - Za * srl / sqrt(num)
#options.CI = [mrll,mrlu];
#options.numdata = num;
titleTxt = 'Mean residual life with %d%s CI' % (100 * p, '%')
res = PlotData(mrl, u, xlab='Threshold',
ylab='Mean Excess', title=titleTxt)
res.workspace = dict(
numdata=num, umin=umin, umax=umax, nu=nu, nmin=nmin, alpha=alpha)
res.children = [
PlotData(vstack([mrll, mrlu]).T, u, xlab='Threshold', title=titleTxt)]
res.plot_args_children = [':r']
if plotflag:
res.plot()
return res
def cav76pdf(t=None, h=None, mom=None, g=None):
"""
CAV76PDF Cavanie et al. (1976) approximation of the density (Tc,Ac)
in a stationary Gaussian transform process X(t) where
Y(t) = g(X(t)) (Y zero-mean Gaussian, X non-Gaussian).
CALL: f = cav76pdf(t,h,[m0,m2,m4],g);
f = density of wave characteristics of half-wavelength
in a stationary Gaussian transformed process X(t),
where Y(t) = g(X(t)) (Y zero-mean Gaussian)
t,h = vectors of periods and amplitudes, respectively.
default depending on the spectral moments
m0,m2,m4 = the 0'th, 2'nd and 4'th moment of the spectral density
with angular frequency.
g = space transformation, Y(t)=g(X(t)), default: g is identity
transformation, i.e. X(t) = Y(t) is Gaussian,
The transformation, g, can be estimated using lc2tr
or dat2tr or given a priori by ochi.
[] = default values are used.
Examples
--------
>>> import wafo.spectrum.models as sm
>>> Sj = sm.Jonswap()
>>> w = np.linspace(0,4,256)
>>> S = Sj.tospecdata(w) #Make spectrum object from numerical values
>>> S = sm.SpecData1D(Sj(w),w) # Alternatively do it manually
>>> mom, mom_txt = S.moment(nr=4, even=True)
>>> f = cav76pdf(mom=mom)
>>> f.plot()
See also
--------
lh83pdf, lc2tr, dat2tr
References
----------
Cavanie, A., Arhan, M. and Ezraty, R. (1976)
"A statistical relationship between individual heights and periods of
storm waves".
In Proceedings Conference on Behaviour of Offshore Structures,
Trondheim, pp. 354--360
Norwegian Institute of Technology, Trondheim, Norway
Lindgren, G. and Rychlik, I. (1982)
Wave Characteristics Distributions for Gaussian Waves --
Wave-lenght, Amplitude and Steepness, Ocean Engng vol 9, pp. 411-432.
"""
# tested on: matlab 5.3 NB! note
# History:
# revised pab 04.11.2000
# - fixed xlabels i.e. f.labx={'Tc','Ac'}
# revised by IR 4 X 2000. fixed transform and normalisation
# using Lindgren & Rychlik (1982) paper.
# At the end of the function there is a text with derivation of the density.
#
# revised by jr 21.02.2000
# - Introduced cell array for f.x for use with pdfplot
# by pab 28.09.1999
m0, m2, m4 = mom
h, t, g = _set_default_t_h_g(t, h, g, m0, m2)
eps4 = 1.0 - m2**2 / (m0 * m4)
alfa = m2 / sqrt(m0 * m4)
if np.any(~np.isreal(eps4)):
raise ValueError('input moments are not correct')
a = len(h)
b = len(t)
der = np.ones((a, 1))
h_lh = g.dat2gauss(h.ravel(), der.ravel())
der = abs(h_lh[1])
h_lh = h_lh[0]
# Normalization + transformation of t and h
pos = 2 / (1 + alfa) # inverse of a fraction of positive maxima
cons = 2 * pi**4 * pos / sqrt(2 * pi) / m4 / sqrt((1 - alfa**2))
# Tm=2*pi*sqrt(m0/m2)/alpha; #mean period between positive maxima
t_lh = t
h_lh = sqrt(m0) * h_lh
# Computation of the distribution
T, H = np.meshgrid(t_lh[1:b], h_lh)
f_th = np.zeros((a, b))
f_th[:, 1:b] = cons * der[:, None] * (H**2 / (T**5)) * np.exp(
-0.5 * (H / T**2)**2. * ((T**2 - pi**2 * m2 / m4)**2 /
(m0 * (1 - alfa**2)) + pi**4 / m4))
f = PlotData(f_th, (t, h),
xlab='Tc',
ylab='Ac',
title='Joint density of (Tc,Ac) - Cavanie et al. (1976)',
plot_kwds=dict(plotflag=1))
return _add_contour_levels(f)
def dispersion_idx(data,
t=None,
u=None,
umin=None,
umax=None,
nu=None,
nmin=10,
tb=1,
alpha=0.05,
plotflag=False):
'''Return Dispersion Index vs threshold
Parameters
----------
data, ti : array_like
data values and sampled times, respectively.
u : array-like
threshold values (default linspace(umin, umax, nu))
umin, umax : real scalars
Minimum and maximum threshold, respectively
(default min(data), max(data)).
nu : scalar integer
number of threshold values (default min(N-nmin,100))
nmin : scalar integer
Minimum number of extremes to include. (Default 10).
tb : Real scalar
Block period (same unit as the sampled times) (default 1)
alpha : real scalar
Confidence coefficient (default 0.05)
plotflag: bool
Returns
-------
DI : PlotData object
Dispersion index
b_u : real scalar
threshold where the number of exceedances in a fixed period (Tb) is
consistent with a Poisson process.
ok_u : array-like
all thresholds where the number of exceedances in a fixed period (Tb)
is consistent with a Poisson process.
Notes
------
DISPRSNIDX estimate the Dispersion Index (DI) as function of threshold.
DI measures the homogenity of data and the purpose of DI is to determine
the threshold where the number of exceedances in a fixed period (Tb) is
consistent with a Poisson process. For a Poisson process the DI is one.
Thus the threshold should be so high that DI is not significantly
different from 1.
The Poisson hypothesis is not rejected if the estimated DI is between:
chi2(alpha/2, M-1)/(M-1)< DI < chi^2(1 - alpha/2, M-1 }/(M - 1)
where M is the total number of fixed periods/blocks -generally
the total number of years in the sample.
Example
-------
>>> import wafo.data
>>> xn = wafo.data.sea()
>>> t, data = xn.T
>>> Ie = findpot(data,t,0,5);
>>> di, u, ok_u = dispersion_idx(data[Ie],t[Ie],tb=100)
>>> h = di.plot() # a threshold around 1 seems appropriate.
>>> round(u*100)/100
1.03
vline(u)
See also
--------
reslife,
fitgenparrange,
extremal_idx
References
----------
Ribatet, M. A.,(2006),
A User's Guide to the POT Package (Version 1.0)
month = {August},
url = {http://cran.r-project.org/}
Cunnane, C. (1979) Note on the poisson assumption in
partial duration series model. Water Resource Research, 15\bold{(2)}
:489--494.}
'''
n = len(data)
if t is None:
ti = arange(n)
else:
ti = arr(t) - min(t)
t1 = np.empty(ti.shape, dtype=int)
t1[:] = np.floor(ti / tb)
if u is None:
sd = np.sort(data)
nmin = max(nmin, 0)
if 2 * nmin > n:
warnings.warn('nmin possibly too large!')
sdmax, sdmin = sd[-nmin], sd[0]
umax = sdmax if umax is None else min(umax, sdmax)
umin = sdmin if umin is None else max(umin, sdmin)
if nu is None:
nu = min(n - nmin, 100)
u = linspace(umin, umax, nu)
nu = len(u)
di = np.zeros(nu)
d = arr(data)
mint = int(min(t1)) # ; % mint should be 0.
maxt = int(max(t1))
M = maxt - mint + 1
occ = np.zeros(M)
for ix, tresh in enumerate(u.tolist()):
excess = (d > tresh)
lambda_ = excess.sum() / M
for block in range(M):
occ[block] = sum(excess[t1 == block])
di[ix] = occ.var() / lambda_
p = 1 - alpha
diLo = _invchi2(1 - alpha / 2, M - 1) / (M - 1)
diUp = _invchi2(alpha / 2, M - 1) / (M - 1)
# Find appropriate threshold
k1, = np.where((diLo < di) & (di < diUp))
if len(k1) > 0:
ok_u = u[k1]
b_di = (di[k1].mean() < di[k1])
k = b_di.argmax()
b_u = ok_u[k]
else:
b_u = ok_u = None
CItxt = '%d%s CI' % (100 * p, '%')
titleTxt = 'Dispersion Index plot'
res = PlotData(di,
u,
title=titleTxt,
labx='Threshold',
laby='Dispersion Index')
#'caption',CItxt);
res.workspace = dict(umin=umin, umax=umax, nu=nu, nmin=nmin, alpha=alpha)
res.children = [
PlotData(vstack([diLo * ones(nu), diUp * ones(nu)]).T,
u,
xlab='Threshold',
title=CItxt)
]
res.plot_args_children = ['--r']
if plotflag:
res.plot(di)
return res, b_u, ok_u
def lh83pdf(t=None, h=None, mom=None, g=None):
"""
LH83PDF Longuet-Higgins (1983) approximation of the density (Tc,Ac)
in a stationary Gaussian transform process X(t) where
Y(t) = g(X(t)) (Y zero-mean Gaussian, X non-Gaussian).
CALL: f = lh83pdf(t,h,[m0,m1,m2],g);
f = density of wave characteristics of half-wavelength
in a stationary Gaussian transformed process X(t),
where Y(t) = g(X(t)) (Y zero-mean Gaussian)
t,h = vectors of periods and amplitudes, respectively.
default depending on the spectral moments
m0,m1,m2 = the 0'th,1'st and 2'nd moment of the spectral density
with angular frequency.
g = space transformation, Y(t)=g(X(t)), default: g is identity
transformation, i.e. X(t) = Y(t) is Gaussian,
The transformation, g, can be estimated using lc2tr
or dat2tr or given apriori by ochi.
Examples
--------
>>> import wafo.spectrum.models as sm
>>> Sj = sm.Jonswap()
>>> w = np.linspace(0,4,256)
>>> S = Sj.tospecdata(w) #Make spectrum object from numerical values
>>> S = sm.SpecData1D(Sj(w),w) # Alternatively do it manually
>>> mom, mom_txt = S.moment(nr=2, even=False)
>>> f = lh83pdf(mom=mom)
>>> f.plot()
See also
--------
cav76pdf, lc2tr, dat2tr
References
----------
Longuet-Higgins, M.S. (1983)
"On the joint distribution wave periods and amplitudes in a
random wave field", Proc. R. Soc. A389, pp 24--258
Longuet-Higgins, M.S. (1975)
"On the joint distribution wave periods and amplitudes of sea waves",
J. geophys. Res. 80, pp 2688--2694
"""
# tested on: matlab 5.3
# History:
# Revised pab 01.04.2001
# - Added example
# - Better automatic scaling for h,t
# revised by IR 18.06.2000, fixing transformation and transposing t and h to fit simpson req.
# revised by pab 28.09.1999
# made more efficient calculation of f
# by Igor Rychlik
m0, m1, m2 = mom
h, t, g = _set_default_t_h_g(t, h, g, m0, m2)
L0 = m0
L1 = m1 / (2 * pi)
L2 = m2 / (2 * pi)**2
eps2 = sqrt((L2 * L0) / (L1**2) - 1)
if np.any(~np.isreal(eps2)):
raise ValueError('input moments are not correct')
const = 4 / sqrt(pi) / eps2 / (1 + 1 / sqrt(1 + eps2**2))
a = len(h)
b = len(t)
der = np.ones((a, 1))
h_lh = g.dat2gauss(h.ravel(), der.ravel())
der = abs(h_lh[1]) # abs(h_lh[:, 1])
h_lh = h_lh[0]
# Normalization + transformation of t and h ???????
# Without any transformation
t_lh = t / (L0 / L1)
# h_lh = h_lh/sqrt(2*L0)
h_lh = h_lh / sqrt(2)
t_lh = 2 * t_lh
# Computation of the distribution
T, H = np.meshgrid(t_lh[1:b], h_lh)
f_th = np.zeros((a, b))
tmp = const * der[:, None] * (H / T)**2 * np.exp(-H**2. * (1 + (
(1 - 1. / T) / eps2)**2)) / ((L0 / L1) * sqrt(2) / 2)
f_th[:, 1:b] = tmp
f = PlotData(f_th, (t, h),
xlab='Tc',
ylab='Ac',
title='Joint density of (Tc,Ac) - Longuet-Higgins (1983)',
plot_kwds=dict(plotflag=1))
return _add_contour_levels(f)
def setUp(self):
x = np.linspace(0, np.pi, 5)
self.d2 = PlotData(np.sin(x), x,
xlab='x', ylab='sin', title='sinus',
plot_args=['r.'])
self.x = x
