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inequalityplot.m

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+function inequalityplot(f,x,y,color,resolution)
+%INEQUALITYPLOT  Inequality plot in 2-D space.
+%
+%   INEQUALITYPLOT(f,x,y,color,resolution) plots the inequality f(x,y) in 
+%   region x(1) <= x <= x(2) and y(1) <= y <= y(2) using specified color.
+%   For multiple inequalities, use & in f. Default color is [0.5,0.75,1]. 
+%   Default resolution is 400.
+%
+%   Example 1: A colored ellipse.
+%  
+%      ellipse = @(x,y) x.^2/4+y.^2<=1;
+%      inequalityplot(ellipse,[-3,3],[-3,3])
+%
+%   Example 2: A colored triangle.
+%
+%      triangle = @(x,y) x>0 & x<1 & y>0 & y<x;
+%      inequalityplot(triangle,[-1,2],[-1,2],'magenta')
+%
+%   Example 3: Area under a Gaussian curve.
+%
+%      g = @(x) 1/sqrt(2*pi)*exp(-x.^2/2);
+%      inequalityplot(@(x,y) y<g(x) & y>0 & x>-2 & x<1,[-3,3],[0,0.5],'c')
+%      hold on; fplot(g,[-3,3],'LineWidth',2); hold off
+%
+%   See also PLOT, FPLOT, AREA, PCOLOR, CONTOUR.
+%
+%   Author:
+%      Ildeberto de los Santos Ruiz
+%      idelossantos@ittg.edu.mx
+
+if nargin < 4 || isempty(color)
+    color = [0.5,0.75,1];
+end
+if isstr(color)
+    switch color
+        case {'r','red'}
+            color = [1,0,0];
+        case {'g','green'}
+            color = [0,1,0];
+        case {'b','blue'}
+            color = [0,0,1];
+        case {'c','cyan'}
+            color = [0,1,1];
+        case {'m','magenta'}
+            color = [1,0,1];
+        case {'y','yellow'}
+            color = [1,1,0];
+        case {'k','black'}
+            color = [0,0,0];
+        case {'w','white'}
+            color = [1,1,1];
+        otherwise
+            color = [0.5,0.75,1];
+    end
+end
+if nargin < 5
+    resolution = 400;
+end
+
+bcolor = get(gca,'Color');
+limx = x;
+limy = y;
+x = linspace(x(1),x(2),resolution);
+y = linspace(y(1),y(2),resolution);
+[x,y] = meshgrid(x,y);
+z = double(f(x,y));
+[r,c] = find(z == 1);
+rlim = min(r):max(r);
+clim = min(c):max(c);
+pcolor(x(rlim,clim),y(rlim,clim),z(rlim,clim));
+colormap([bcolor;color])
+axis([limx,limy])
+shading flat