PDL::Primitive - primitive operations for pdl |
PDL::Primitive - primitive operations for pdl
This module provides some primitive and useful functions defined using PDL::PP and able to use the new indexing tricks.
See PDL::Indexing for how to use indices creatively. For explanation of the signature format, see PDL::PP.
use PDL::Primitive;
Signature: (a(n); b(n); [o]c())
Inner product over one dimension
c = sum_i a_i * b_i
Signature: (a(n); b(m); [o]c(n,m))
outer product over one dimension
Naturally, it is possible to achieve the effects of outer
product simply by threading over the ``*
''
operator but this function is provided for convenience.
Signature: (a(x,y),b(y,z),[o]c(x,z))
Matrix multiplication
We peruse the inner product to define matrix multiplication via a threaded inner product
Signature: (a(n); b(n); c(n); [o]d())
Weighted (i.e. triple) inner product
d = sum_i a(i) b(i) c(i)
Signature: (a(n); b(n,m); c(m); [o]d())
Inner product of two vectors and a matrix
d = sum_ij a(i) b(i,j) c(j)
Note that you should probably not thread over a
and c
since that would be
very wasteful. Instead, you should use a temporary for b*c
.
Signature: (a(n,m); b(n,m); [o]c())
Inner product over 2 dimensions.
Equivalent to
$c = inner($a->clump(2), $b->clump(2))
Signature: (a(j,n); b(n,m); c(m,k); [t]tmp(n,k); [o]d(j,k)))
Efficient Triple matrix product a*b*c
Efficiency comes from by using the temporary tmp
. This operation only
scales as N**3
whereas threading using inner2 would scale
as N**4
.
The reason for having this routine is that you do not need to
have the same thread-dimensions for tmp
as for the other arguments,
which in case of large numbers of matrices makes this much more
memory-efficient.
It is hoped that things like this could be taken care of as a kind of closures at some point.
Signature: (a(tri=3); b(tri); [o] c(tri))
Cross product of two 3D vectors
After
$c = crossp $a, $b
the inner product $c*$a
and $c*$b
will be zero, i.e. $c
is
orthogonal to $a
and $b
Signature: (vec(n); [o] norm(n))
Normalises a vector to unit Euclidean length
Signature: (a(); int ind(); [o] sum(m))
Threaded Index Add: Add a
to the ind
element of sum
, i.e:
sum(ind) += a
Simple Example:
$a = 2; $ind = 3; $sum = zeroes(10); indadd($a,$ind, $sum); print $sum #Result: ( 2 added to element 3 of $sum) # [0 0 0 2 0 0 0 0 0 0]
Threaded Example:
$a = pdl( 1,2,3); $ind = pdl( 1,4,6); $sum = zeroes(10); indadd($a,$ind, $sum); print $sum."\n"; #Result: ( 1, 2, and 3 added to elements 1,4,6 $sum) # [0 1 0 0 2 0 3 0 0 0]
Signature: (a(m); kern(p); [o]b(m); int reflect)
1d convolution along first dimension
$con = conv1d sequence(10), pdl(-1,0,1), {Boundary => 'reflect'};
By default, periodic boundary conditions are assumed (i.e. wrap around).
Alternatively, you can request reflective boundary conditions using
the Boundary
option:
{Boundary => 'reflect'} # case in 'reflect' doesn't matter
The convolution is performed along the first dimension. To apply it across another dimension use the slicing routines, e.g.
$b = $a->mv(2,0)->conv1d($kernel)->mv(0,2); # along third dim
This function is useful for threaded filtering of 1D signals.
Compare also conv2d, convolve, fftconvolve, fftwconv, rfftwconv
Signature: (a(); b(n); [o] c())
test if a is in the set of values b
$goodmsk = $labels->in($goodlabels); print pdl(4,3,1)->in(pdl(2,3,3)); [0 1 0]
in
is akin to the is an element of of set theory. In priciple,
PDL threading could be used to achieve its functionality by using a
construct like
$msk = ($labels->dummy(0) == $goodlabels)->orover;
However, in
doesn't create a (potentially large) intermediate
and is generally faster.
return all unique elements of a piddle
The unique elements are returned in ascending order.
print pdl(2,2,2,4,0,-1,6,6)->uniq; [-1 0 2 4 6]
Note: The returned pdl is 1D; any structure of the input piddle is lost.
Signature: (a(); b(); [o] c())
clip $a
by $b
($b
is upper bound)
Signature: (a(); b(); [o] c())
clip $a
by $b
($b
is lower bound)
Clip a piddle by (optional) upper or lower bounds.
$b = $a->clip(0,3); $c = $a->clip(undef, $x);
Signature: (a(n); wt(n); avg(); [o]b(); int deg)
Weighted statistical moment of given degree
This calculates a weighted statistic over the vector a
.
The formula is
b() = (sum_i wt_i * (a_i ** degree - avg)) / (sum_i wt_i)
Signature: (a(n); w(n); int+ [o]avg(); int+ [o]rms(); int+ [o]min(); int+ [o]max(); int+ [o]adev())
Calculate useful statistics over a dimension of a piddle
($mean, $rms, $median, $min, $max, $adev) = statover($piddle, $weights);
This utility function calculates various useful quantities of a piddle. These are the mean:
MEAN = sum (x)/ N
with N
being the number of elements in x, the root mean
square deviation from the mean, RMS, given as,
RMS = sqrt(sum( (x-mean(x))^2 )/(N-1));
Note the use of N-1
which for almost all cases should be
the right normalisation factor. The routine also returns
the median, minimum and maximum of the piddle as well as
the mean absolute deviation, defined as:
ADEV = sqrt(sum( abs(x-mean(x)) )/N)
note here that we use the mean and not the median. This could possibly be changed in future versions of the code.
This operator is a projection operator so the calculation
will take place over the final dimension. Thus if the input
is N-dimensional each returned value will be N-1 dimensional,
to calculate the statistics for the entire piddle either
use clump(-1)
directly on the piddle or call stats
.
Calculates useful statistics on a piddle
($mean,$rms,$median,$min,$max) = stats($piddle,[$weights]);
This utility calculates all the most useful quantities in one call.
Note: The RMS value that this function returns in the RMS deviation from the mean, also known as the population standard- deviation.
Signature: (in(n); int+[o] hist(m); double step; double min; int msize => m)
Calculates a histogram for given stepsize and minimum.
$h = histogram($data, $step, $min, $numbins); $hist = zeroes $numbins; # Put histogram in existing piddle. histogram($data, $hist, $step, $min, $numbins);
The histogram will contain $numbins
bins starting from $min
, each
$step
wide. The value in each bin is the number of
values in $data
that lie within the bin limits.
Data below the lower limit is put in the first bin, and data above the upper limit is put in the last bin.
The output is reset in a different threadloop so that you
can take a histogram of $a(10,12)
into $b(15)
and get the result
you want.
Use hist instead for a high-level interface.
perldl> p histogram(pdl(1,1,2),1,0,3) [0 2 1]
Signature: (in(n); float+ wt(n);float+[o] hist(m); double step; double min; int msize => m)
Calculates a histogram from weighted data for given stepsize and minimum.
$h = whistogram($data, $weights, $step, $min, $numbins); $hist = zeroes $numbins; # Put histogram in existing piddle. whistogram($data, $weights, $hist, $step, $min, $numbins);
The histogram will contain $numbins
bins starting from $min
, each
$step
wide. The value in each bin is the sum of the values in $weights
that correspond to values in $data
that lie within the bin limits.
Data below the lower limit is put in the first bin, and data above the upper limit is put in the last bin.
The output is reset in a different threadloop so that you
can take a histogram of $a(10,12)
into $b(15)
and get the result
you want.
perldl> p whistogram(pdl(1,1,2), pdl(0.1,0.1,0.5), 1, 0, 4) [0 0.2 0.5 0]
Signature: (ina(n); inb(n); int+[o] hist(ma,mb); double stepa; double mina; int masize => ma; double stepb; double minb; int mbsize => mb;)
Calculates a 2d histogram.
$h = histogram2d($datax, $datay, $stepx, $minx, $nbinx, $stepy, $miny, $nbiny); $hist = zeroes $nbinx, $nbiny; # Put histogram in existing piddle. histogram2d($datax, $datay, $hist, $stepx, $minx, $nbinx, $stepy, $miny, $nbiny);
The histogram will contain $nbinx
x $nbiny
bins, with the lower
limits of the first one at ($minx, $miny)
, and with bin size
($stepx, $stepy)
.
The value in each bin is the number of
values in $datax
and $datay
that lie within the bin limits.
Data below the lower limit is put in the first bin, and data above the upper limit is put in the last bin.
perldl> p histogram2d(pdl(1,1,1,2,2),pdl(2,1,1,1,1),1,0,3,1,0,3) [ [0 0 0] [0 2 2] [0 1 0] ]
Signature: (ina(n); inb(n); float+ wt(n);float+[o] hist(ma,mb); double stepa; double mina; int masize => ma; double stepb; double minb; int mbsize => mb;)
Calculates a 2d histogram from weighted data.
$h = whistogram2d($datax, $datay, $weights, $stepx, $minx, $nbinx, $stepy, $miny, $nbiny); $hist = zeroes $nbinx, $nbiny; # Put histogram in existing piddle. whistogram2d($datax, $datay, $weights, $hist, $stepx, $minx, $nbinx, $stepy, $miny, $nbiny);
The histogram will contain $nbinx
x $nbiny
bins, with the lower
limits of the first one at ($minx, $miny)
, and with bin size
($stepx, $stepy)
.
The value in each bin is the sum of the values in
$weights
that correspond to values in $datax
and $datay
that lie within the bin limits.
Data below the lower limit is put in the first bin, and data above the upper limit is put in the last bin.
perldl> p whistogram2d(pdl(1,1,1,2,2),pdl(2,1,1,1,1),pdl(0.1,0.2,0.3,0.4,0.5),1,0,3,1,0,3) [ [ 0 0 0] [ 0 0.5 0.9] [ 0 0.1 0] ]
Signature: ([o]x(n))
Constructor - a vector with Fibonacci's sequence
Signature: (a(n); b(m); [o] c(mn))
append two or more piddles by concatenating along their first dimensions
$a = ones(2,4,7); $b = sequence 5; $c = $a->append($b); # size of $c is now (7,4,7) (a jumbo-piddle ;)
append
appends two piddles along their first dims. Rest of the dimensions
must be compatible in the threading sense. Resulting size of first dim is
the sum of the sizes of the first dims of the two argument piddles -
ie n + m
.
$c = $a->glue(<dim>,$b,...)
Glue two or more PDLs together along an arbitrary dimension (N-D L<append|append>).
Sticks $a, $b, and all following arguments together using a combination
of xchg()
and append(). All other dimensions must be compatible in the
threading sense.
glue
is implemented in pdl, and should probably be updated (one day) to a
pure PP function.
Signature: ([o,nc]a(n))
Internal routine
axisvalues
is the internal primitive that implements
axisvals
and alters its argument.
Constructor which returns piddle of random numbers
$a = random([type], $nx, $ny, $nz,...); $a = random $b;
etc (see zeroes).
This is the uniform distribution between 0 and 1 (assumedly
excluding 1 itself). The arguments are the same as zeroes
(q.v.) - i.e. one can specify dimensions, types or give
a template.
You can use the perl function srand to seed the random generator. For further details consult Perl's srand documentation.
Constructor which returns piddle of random numbers
$a = randsym([type], $nx, $ny, $nz,...); $a = randsym $b;
etc (see zeroes).
This is the uniform distribution between 0 and 1 (excluding both 0 and
1, cf random). The arguments are the same as zeroes
(q.v.) -
i.e. one can specify dimensions, types or give a template.
You can use the perl function srand to seed the random generator. For further details consult Perl's srand documentation.
Constructor which returns piddle of Gaussian random numbers
$a = grandom([type], $nx, $ny, $nz,...); $a = grandom $b;
etc (see zeroes).
This is generated using the math library routine ndtri
.
Mean = 0, Stddev = 1
You can use the perl function srand to seed the random generator. For further details consult Perl's srand documentation.
Signature: (i(); x(n); int [o]ip())
routine for searching 1D values i.e. step-function interpolation.
$inds = vsearch($vals, $xs);
Returns for each value of $vals
the index of the least larger member
of $xs
(which need to be in increasing order). If the value is larger
than any member of $xs
, the index to the last element of $xs
is
returned.
This function is useful e.g. when you have a list of probabilities for events and want to generate indices to events:
$a = pdl(.01,.86,.93,1); # Barnsley IFS probabilities cumulatively $b = random 20; $c = vsearch($b, $a); # Now, $c will have the appropriate distr.
It is possible to use the cumusumover function to obtain cumulative probabilities from absolute probabilities.
Signature: (xi(); x(n); y(n); [o] yi(); int [o] err())
routine for 1D linear interpolation
( $yi, $err ) = interpolate($xi, $x, $y)
Given a set of points ($x,$y)
, use linear interpolation
to find the values $yi
at a set of points $xi
.
interpolate
uses a binary search to find the suspects, er...,
interpolation indices and therefore abscissas (ie $x
)
have to be strictly ordered (increasing or decreasing).
For interpolation at lots of
closely spaced abscissas an approach that uses the last index found as
a start for the next search can be faster (compare Numerical Recipes
hunt
routine). Feel free to implement that on top of the binary
search if you like. For out of bounds values it just does a linear
extrapolation and sets the corresponding element of $err
to 1,
which is otherwise 0.
See also interpol, which uses the same routine, differing only in the handling of extrapolation - an error message is printed rather than returning an error piddle.
Signature: (xi(); x(n); y(n); [o] yi())
routine for 1D linear interpolation
$yi = interpol($xi, $x, $y)
interpol
uses the same search method as interpolate,
hence $x
must be strictly ordered (either increasing or decreasing).
The difference occurs in the handling of out-of-bounds values; here
an error message is printed.
Interpolate values from an N-D piddle
$source = 10*xvals(10,10) + yvals(10,10); $index = pdl([[2.2,3.5],[4.1,5.0]],[[6.0,7.4],[8,9]]); print $source->interpND( $index );
InterpND acts like indexND, collapsing $index
by lookup
into $source
; but it does interpolation, rather than straight
lookup, into $source
. Several options may be passed in via an
options hash. By default, linear or sample interpolation is used, with
constant value outside the boundaries of the source pdl. No flowback
occurs, because the output is interpolated rather than indexed.
All the interpolation methods treat the pixels as value-centered, so
the sample
method will return $a->(0) for coordinate values on
the set [-0.5,0.5), and the linear
method will return $a->(1) for
a coordinate value of exactly 1.5.
Allowable options:
=over 3
Converts a one dimensional index piddle to a set of ND coordinates
@coords=one2nd($a, $indices)
returns an array of piddles containing the ND indexes corresponding to
the one dimensional list indices. The indices are assumed to correspond
to array $a
clumped using clump(-1)
. This routine is used in
whichND,
but is useful on its own occasionally.
perldl> $a=pdl [[[1,2],[-1,1]], [[0,-3],[3,2]]]; $c=$a->clump(-1) perldl> $maxind=maximum_ind($c); p $maxind; 6 perldl> print one2nd($a, maximum_ind($c)) 0 1 1 perldl> p $a->at(0,1,1) 3
Signature: (mask(n); int [o] inds(m))
Returns piddle of indices of non-zero values.
$i = which($mask);
returns a pdl with indices for all those elements that are nonzero in the mask. Note that the returned indices will be 1D. If you want to index into the original mask or a similar piddle remember to flatten it before calling index:
$data = random 5, 5; $idx = which $data > 0.5; # $idx is now 1D $bigsum = $data->flat->index($idx)->sum; # flatten before indexing
Compare also where for similar functionality.
If you want to return both the indices of non-zero values and the complement, use the function which_both.
perldl> $x = sequence(10); p $x [0 1 2 3 4 5 6 7 8 9] perldl> $indx = which($x>6); p $indx [7 8 9]
Signature: (mask(n); int [o] inds(m); int [o]notinds(q))
Returns piddle of indices of non-zero values and their complement
($i, $c_i) = which_both($mask);
This works just as which, but the complement of $i
will be in
$c_i
.
perldl> $x = sequence(10); p $x [0 1 2 3 4 5 6 7 8 9] perldl> ($small, $big) = which_both ($x >= 5); p "$small\n $big" [5 6 7 8 9] [0 1 2 3 4]
Returns indices to non-zero values or those values from another piddle.
$i = $x->where($x+5 > 0); # $i contains elements of $x # where mask ($x+5 > 0) is 1
Note: $i
is always 1-D, even if $x
is >1-D. The first argument
(the values) and the second argument (the mask) currently have to have
the same initial dimensions (or horrible things happen).
It is also possible to use the same mask for several piddles with the same call:
($i,$j,$k) = where($x,$y,$z, $x+5>0);
Returns the coordinates for non-zero values.
For historical reasons the return value is different in list and scalar context. In scalar context, you get back a PDL containing coordinates suitable for use in indexND or range; in list context, the coordinates are broken out into separate PDLs.
$coords = whichND($mask);
returns a PDL containing the coordinates of the elements that are non-zero
in $mask
, suitable for use in indexND. The 0th dimension contains the
full coordinate listing of each point; the 1st dimension lists all the points.
For example, if $mask has rank 4 and 100 matching elements, then $coords has
dimension 4x100.
@coords=whichND($mask);
returns a perl list of piddles containing the coordinates of the
elements that are non-zero in $mask
. Each element corresponds to a
particular index dimension. For example, if $mask has rank 4 and 100
matching elements, then @coords has 4 elements, each of which is a pdl
of size 100.
perldl> $a=sequence(10,10,3,4) perldl> ($x, $y, $z, $w)=whichND($a == 203); p $x, $y, $z, $w [3] [0] [2] [0] perldl> print $a->at(list(cat($x,$y,$z,$w))) 203
Copyright (C) Tuomas J. Lukka 1997 (lukka@husc.harvard.edu) Contributions by Christian Soeller (c.soeller@auckland.ac.nz), Karl Glazebrook (kgb@aaoepp.aao.gov.au), and Craig DeForest (deforest@boulder.swri.edu) All rights reserved. There is no warranty. You are allowed to redistribute this software / documentation under certain conditions. For details, see the file COPYING in the PDL distribution. If this file is separated from the PDL distribution, the copyright notice should be included in the file.
PDL::Primitive - primitive operations for pdl |