Compute function of two variables

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Justin Bruh
Justin Bruh 2017-1-28
回答： Justin Bruh 2017-1-28
I have a function Ux=f(x,t) where f(x,t) is an infinite sine series (which I've truncated at 50 terms). I want to find the values of Ux at every x and t and out put it as a matrix (# of x values X #of t values), then plot a contour of where Ux is zero on a 2-D plot of x vs t (I want t on the y-axis). Here's what I've tried so far:
syms x t
%Establish An Coefficients
n=0;
for m=1:1:50
n=n+1;
if n==2
A(n)=0.5;
else
A(n)=(-4*sin(.5*pi*m))/((pi*m^2)-(4*pi));
end
end
%Determine T(t) Values for each Value of An
index=0;
for n=1:1:50
index=index+1;
T(index)=exp(-(n^2)*(pi^2)*t);
end
%Find values of X'(x)
index=0;
for n=1:1:50
index=index+1;
dX(index)=(A(n))*(n*pi)*cos(n*pi*x);
end
Ux=(sum(dX.*T));
x=.2:.01:.75;
t=0:.005:.5;
Flux=eval(Ux);
[A,B] = meshgrid(x,t);
v=[0,0];
figure
contour(A,B,Flux,v)
so x is 1 X 56 matrix and t is a 1 X 101 matrix. My understanding is that to make the contour part work I need 'Flux' to output as a 56 X 101 matrix. I keep getting the following error:
Error in sym/eval (line 11)
s = evalin('caller',vectorize(map2mat(char(x))));
Error in zeroflux (line 42)
Flux=eval(Ux);
  2 个评论
Jan
Jan 2017-1-28
Is this the complete error message? It tells only, where the problem occurres, but not, what the problem is.
Justin Bruh
Justin Bruh 2017-1-28
That is the complete error message

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回答（1 个）

Justin Bruh
Justin Bruh 2017-1-28
I've figured it out. Everything down to the end of the 3 loops is the same. Then I added this fourth loop:
index1=0;
index2=0;
for t=0:.005:1
index1=1+index1;
index2=0;
for x=0:0.01:1
index2=index2+1;
Ux(index1,index2)=eval(sum(dX.*T));
end
end
x=0:.01:1;
t=0:.005:1;
[A,B] = meshgrid(x,t);
v=[0,0];
figure
contour(A,B,Ux,v)

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