Error: The size of X must match the size of U or the number of columns of U.
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geometry geometry
on 14 May 2017
Commented: geometry geometry
on 15 May 2017
What's the problem with this code? when I run it the following Error occurs:
Error using quiver
The size of X must match the size of U or the number of columns of U.
syms x y;
f=input('enter function: ','s');
f = symfun(eval(f), [x y]);
u=-diff(f,x);
v=-diff(f,y);
[X,Y]=meshgrid(-10:.5:10);
quiver(X,Y,u,v);
2 Comments
Accepted Answer
Stephen23
on 14 May 2017
Edited: Stephen23
on 14 May 2017
There is no need to make the code slower and more complicated by using syms and eval. Exactly as I wrote in my answer to your related question, simple numeric calculations will do everything you need:
% str = input('enter a function in x and y: ','s');
str = 'log(x^2+y^2)';
fun = str2func(['@(x,y)',str]);
[X,Y] = meshgrid(-10:.51:10);
[DX,DY] = gradient(arrayfun(fun,X,Y));
quiver(X,Y,DX,DY,5);
3 Comments
Star Strider
on 14 May 2017
This was a previous attempt by OP (in another Question) that apparently did not work.
OP is using another approach here, so it is best to follow that approach.
More Answers (1)
Star Strider
on 14 May 2017
Remember that ‘u’ and ‘v’ are also functions of (x,y), so use them as ‘u(x,y)’ and ‘v(x,y)’. With one change (changing the step in the meshgrid vector to 0.51 to prevent ‘division by zero’ errors), this works:
syms x y;
% f=input('enter function: ','s');
f = 'log(x^2+y^2)';
f = symfun(eval(f), [x y]);
u=-diff(f,x);
v=-diff(f,y);
[X,Y]=meshgrid(-10:.51:10);
quiver(X,Y,u(X,Y),v(X,Y),5);
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