# 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 CommentsShowHide 1 older comment
geometry geometry on 14 May 2017
could you please fix the code? (I'm new to matlab) thanks;

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);
quiver(X,Y,DX,DY,5);
geometry geometry on 15 May 2017
Thanks; sorry to make a similar post.
after you changed the name of that post I thought someone deleted that post! hence I made this post.

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);