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## Copyright (C) 2007, 2008 David Bateman
##
## This file is part of Octave.
##
## Octave is free software; you can redistribute it and/or modify it
## under the terms of the GNU General Public License as published by
## the Free Software Foundation; either version 3 of the License, or (at
## your option) any later version.
##
## Octave is distributed in the hope that it will be useful, but
## WITHOUT ANY WARRANTY; without even the implied warranty of
## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
## General Public License for more details.
##
## You should have received a copy of the GNU General Public License
## along with Octave; see the file COPYING. If not, see
## <http://www.gnu.org/licenses/>.
function interpimages (nm, typ)
bury_output ();
if (strcmp (typ, "png"))
set (0, "defaulttextfontname", "*");
endif
if (strcmp (typ, "txt"))
image_as_txt (nm);
elseif (strcmp (nm, "interpft"))
t = 0 : 0.3 : pi; dt = t(2)-t(1);
n = length (t); k = 100;
ti = t(1) + [0 : k-1]*dt*n/k;
y = sin (4*t + 0.3) .* cos (3*t - 0.1);
yp = sin (4*ti + 0.3) .* cos (3*ti - 0.1);
plot (ti, yp, 'g', ti, interp1(t, y, ti, 'spline'), 'b', ...
ti, interpft (y, k), 'c', t, y, 'r+');
legend ('sin(4t+0.3)cos(3t-0.1)','spline','interpft','data');
print (cstrcat (nm, ".", typ), cstrcat ("-d", typ))
elseif (strcmp (nm, "interpn"))
x = y = z = -1:1;
f = @(x,y,z) x.^2 - y - z.^2;
[xx, yy, zz] = meshgrid (x, y, z);
v = f (xx,yy,zz);
xi = yi = zi = -1:0.1:1;
[xxi, yyi, zzi] = ndgrid (xi, yi, zi);
vi = interpn(x, y, z, v, xxi, yyi, zzi, 'spline');
mesh (zi, yi, squeeze (vi(1,:,:)));
print (cstrcat (nm, ".", typ), cstrcat ("-d", typ))
elseif (strcmp (nm, "interpderiv1"))
t = -2:2;
dt = 1;
ti =-2:0.025:2;
dti = 0.025;
y = sign(t);
ys = interp1(t,y,ti,'spline');
yp = interp1(t,y,ti,'pchip');
plot (ti, ys,'r-', ti, yp,'g-');
legend('spline','pchip', 4);
print (cstrcat (nm, ".", typ), cstrcat ("-d", typ))
elseif (strcmp (nm, "interpderiv2"))
t = -2:2;
dt = 1;
ti =-2:0.025:2;
dti = 0.025;
y = sign(t);
ddys = diff(diff(interp1(t,y,ti,'spline'))./dti)./dti;
ddyp = diff(diff(interp1(t,y,ti,'pchip'))./dti)./dti;
plot (ti(2:end-1),ddys,'r*', ti(2:end-1),ddyp,'g+');
legend('spline','pchip');
print (cstrcat (nm, ".", typ), cstrcat ("-d", typ))
endif
bury_output ();
endfunction
## Use this function before plotting commands and after every call to
## print since print() resets output to stdout (unfortunately, gnpulot
## can't pop output as it can the terminal type).
function bury_output ()
f = figure (1);
set (f, "visible", "off");
endfunction
## generate something for the texinfo @image command to process
function image_as_txt(nm)
fid = fopen (sprintf ("%s.txt", nm), "wt");
fputs (fid, "\n");
fputs (fid, "+---------------------------------+\n");
fputs (fid, "| Image unavailable in text mode. |\n");
fputs (fid, "+---------------------------------+\n");
fclose (fid);
endfunction
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