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Manpages BasicSection: User Contributed Perl Documentation (3)Updated: 2001-10-25 Index Return to Main Contents NAMEPDL::Basic - Basic utility functions for PDLDESCRIPTIONThis module contains basic utility functions for creating and manipulating piddles. Most of these functions are simplified interfaces to the more flexible functions in the modules PDL::Primitive and PDL::Slices.SYNOPSISuse PDL::Basic; FUNCTIONSxvalsFills a piddle with X index values
$x = xvals($somearray); $x = xvals([OPTIONAL TYPE],$nx,$ny,$nz...);etc. see zeroes.
perldl> print xvals zeroes(5,10) [ [0 1 2 3 4] [0 1 2 3 4] [0 1 2 3 4] [0 1 2 3 4] [0 1 2 3 4] [0 1 2 3 4] [0 1 2 3 4] [0 1 2 3 4] [0 1 2 3 4] [0 1 2 3 4] ] yvalsFills a piddle with Y index values
$x = yvals($somearray); yvals(inplace($somearray)); $x = yvals([OPTIONAL TYPE],$nx,$ny,$nz...);etc. see zeroes.
perldl> print yvals zeroes(5,10) [ [0 0 0 0 0] [1 1 1 1 1] [2 2 2 2 2] [3 3 3 3 3] [4 4 4 4 4] [5 5 5 5 5] [6 6 6 6 6] [7 7 7 7 7] [8 8 8 8 8] [9 9 9 9 9] ] zvalsFills a piddle with Z index values
$x = zvals($somearray); zvals(inplace($somearray)); $x = zvals([OPTIONAL TYPE],$nx,$ny,$nz...);etc. see zeroes.
perldl> print zvals zeroes(3,4,2) [ [ [0 0 0] [0 0 0] [0 0 0] [0 0 0] ] [ [1 1 1] [1 1 1] [1 1 1] [1 1 1] ] ] xlinvalsX axis values between endpoints (see xvals).
$a = zeroes(100,100); $x = $a->xlinvals(0.5,1.5); $y = $a->ylinvals(-2,-1); # calculate Z for X between 0.5 and 1.5 and # Y between -2 and -1. $z = f($x,$y);"xlinvals", "ylinvals" and "zlinvals" return a piddle with the same shape as their first argument and linearly scaled values between the two other arguments along the given axis. ylinvalsY axis values between endpoints (see yvals).See xlinvals for more information. zlinvalsZ axis values between endpoints (see zvals).See xlinvals for more information. histCreate histogram of a piddle
$hist = hist($data,[$min,$max,$step]); ($xvals,$hist) = hist($data,[$min,$max,$step]);If requested, $xvals gives the computed bin centres A nice idiom (with PDL::Graphics::PGPLOT) is
bin hist $data; # Plot histogram perldl> p $y [13 10 13 10 9 13 9 12 11 10 10 13 7 6 8 10 11 7 12 9 11 11 12 6 12 7] perldl> $h = hist $y,0,20,1; # hist with step 1, min 0 and 20 bins perldl> p $h [0 0 0 0 0 0 2 3 1 3 5 4 4 4 0 0 0 0 0 0] whistCreate a weighted histogram of a piddle
$hist = whist($data, $wt, [$min,$max,$step]); ($xvals,$hist) = whist($data, $wt, [$min,$max,$step]);If requested, $xvals gives the computed bin centres. $data and $wt should have the same dimensionality and extents. A nice idiom (with PDL::Graphics::PGPLOT) is
bin whist $data, $wt; # Plot histogram perldl> p $y [13 10 13 10 9 13 9 12 11 10 10 13 7 6 8 10 11 7 12 9 11 11 12 6 12 7] perldl> $wt = grandom($y->nelem) perldl> $h = whist $y, $wt, 0, 20, 1 # hist with step 1, min 0 and 20 bins perldl> p $h [0 0 0 0 0 0 -0.49552342 1.7987439 0.39450696 4.0073722 -2.6255299 -2.5084501 2.6458365 4.1671676 0 0 0 0 0 0] sequenceCreate array filled with a sequence of values
$a = sequence($b); $a = sequence [OPTIONAL TYPE], @dims;etc. see zeroes.
perldl> p sequence(10) [0 1 2 3 4 5 6 7 8 9] perldl> p sequence(3,4) [ [ 0 1 2] [ 3 4 5] [ 6 7 8] [ 9 10 11] ] rvalsFills a piddle with radial distance values from some centre.
$r = rvals $piddle,{OPTIONS}; $r = rvals [OPTIONAL TYPE],$nx,$ny,...{OPTIONS}; Options: Centre => [$x,$y,$z...] # Specify centre Center => [$x,$y.$z...] # synonym. Squared => 1 # return distance squared (i.e., don't take the square root) perldl> print rvals long,7,7,{Centre=>[2,2]} [ [2 2 2 2 2 3 4] [2 1 1 1 2 3 4] [2 1 0 1 2 3 4] [2 1 1 1 2 3 4] [2 2 2 2 2 3 4] [3 3 3 3 3 4 5] [4 4 4 4 4 5 5] ]For a more general metric, one can define, e.g.,
sub distance { my ($a,$centre,$f) = @_; my ($r) = $a->allaxisvals-$centre; $f->($r); } sub l1 { sumover(abs($_[0])); } sub euclid { use PDL::Math 'pow'; pow(sumover(pow($_[0],2)),0.5); } sub linfty { maximum(abs($_[0])); }so now
distance($a, $centre, \&euclid);will emulate rvals, while "\&l1" and "\&linfty" will generate other well-known norms. axisvalsFills a piddle with index values on Nth dimension
$z = axisvals ($piddle, $nth);This is the routine, for which xvals, yvals etc are mere shorthands. "axisvals" can be used to fill along any dimension. Note the 'from specification' style (see zeroes) is not available here, for obvious reasons. allaxisvalsGenerates a piddle with index values
$z = allaxisvals ($piddle);"allaxisvals" produces an array with axis values along each dimension, adding an extra dimension at the start. "allaxisvals($piddle)->slice("($nth)")" will produce the same result as "axisvals($piddle,$nth)" (although with extra work and not inplace). It's useful when all the values will be required, as in the example given of a generalized rvals. transposetranspose rows and columns.
$b = transpose($a); $b = ~$a;Also bound to the "~" unary operator in PDL::Matrix.
perldl> $a = sequence(3,2) perldl> p $a [ [0 1 2] [3 4 5] ] perldl> p transpose( $a ) [ [0 3] [1 4] [2 5] ]
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