How I can integrate function if I have two variables?

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Subinuer
Subinuer 2014-6-30
评论： Star Strider 2021-3-22
Hi:
I am using trapz to integrate my function, but in my function I have two variables, what should I do if I want to integrate only one variable and keep the other one? if anyone can help me, I will be appreciate it.
Thank you
Subinuer
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Laurence Lurio
Laurence Lurio 2017-2-2
编辑：Laurence Lurio 2017-2-2
Suppose you have f(x,y) and you want to integrate from A to B over x with y=y0. Then
y=y0
fun2=@(x)fun(x,y0)
result=integral(fun2,A,B)

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Star Strider
Star Strider 2014-6-30
If you have already evaluated your function and have a matrix of (x,y) values for it, you can use trapz to integrate it in the dimension you want.
Example:
f = @(x,y) 3*x.^2 + 5*y.^3;
x = 0:0.1:5;
y = 0:0.1:7;
[X, Y] = meshgrid(x,y);
fmtx = f(X,Y);
fxint = trapz(x,fmtx,2);
figure(1)
surfc(X,Y,fmtx)
grid on
xlabel('X')
ylabel('Y')
Otherwise, you need to do the integration with the Symbolic Math Toolbox:
syms x y
f(x,y) = 3*x.^2 + 5*y.^3;
fint = int(f, x)
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Sinipelto
Sinipelto 2021-3-22
I was using "integral" function which didnt work, when I switched to this "int" function, it started working. Thanks!
Star Strider
Star Strider 2021-3-22
My pleasure!
The trapz function integrates vectors and matrices numerically.
The integral function integrates functions numerically.
The int function integrates symbolic expressions and functions, and vpaintegral integrates them numerically.

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