Plot a matrix which has functions
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I have these functions (in a script):
fx = @ (x) exp(-x.^2);
f1x = @ (x) 1/(x.^2+1);
fpx = f1x/int(f1x,x,0,1)
I want to plot a table with {fx,fpx} when {x,0,1}.
How can I do this?
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Walter Roberson
le 26 Jan 2011
int() is a routine that applies to symbolic expressions, not to function handles. Do you have access to the Symbolic Toolkit? If not, then you will need to do a numeric integration such as with trapz or quadl
If you are using the symbolic toolbox, you would rewrite all three clauses. If you are not, then your last clause should not be
fpx=f1x/int(f1x,x,0,1)
but rather something like
fpx = @(x) f1x(x) ./ quadl(f1x,0,1)
It should not, however, be something like
fpx = @(x) double(subs(f1x,'x',x)) ./ double(int(f1x,x,0,1))
which is close but has the problem that the "x" in the call to "int" needs to be the symbolic variable to integrate with respect to, and should not be the particular value of x that you are using to evaluate f1x in the numerator. You could, however, use:
fpx = @(x) double(subs(f1x,'x',x)) ./ double(int(f1x,'x',0,1))
Once you have constructed fpx to be a function of x, you could construct your table as
SubDivisons = 250;
xvals = linspace(0,1,SubDivisions) .';
YourTable = [fx(xvals), fpx(xvals)];
plot(xvals, YourTable);
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Paulo Silva
le 26 Jan 2011
disp('Executing the function, please wait')
steps=0.05;
%increase steps to speed up execution, accuracy will be lower
%decrease steps to improve accuracy, you have to wait more time
x=0:steps:1;
fx=inline('exp(-x.^2)');
f1x=inline('1./(x.^2+1)');
fpx=sym(f1x)./int(sym(f1x));
fpx=subs(fpx,'x',x);
fx=subs(fx,'x',x);
Table=[fx;fpx];
plot(fx,fpx)
disp('All done, you can find the result in variable Table')
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Paulo Silva
le 27 Jan 2011
I have no idea about what could be wrong, it's working here in Matlab 2008b (32bits), here's the result http://img254.imageshack.us/img254/5666/46107520.jpg
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