Don't know what is wrong with this double integral code

3 次查看（过去 30 天）
Ignacio Ayerbe Pérez-Piñar
回答： Bjorn Gustavsson 2021-2-3
I'm trying to write a script that can calculate the double integral of a function. What I want to do is this:
  • move along the y-axis.
  • for each value of y, I calculate the area of the cross-section of the 3D graph, which is the integral of the function for x at that specific value of y.
  • I multiply this area by a small increment in y to get an elemental volume.
  • I add up all these volumes up to get the final volume under the graph, which is equal to the double integral.
I don't know why my code isn't giving me the write answer for sin(x)*sin(y) between 0 and pi for x limits and 0 and pi for y limits.
I attach my code as a .m file and also below:
f = @(a, b) sin(a)*sin(b);
x0 = 0;
xn = pi; % Integral limits
n = 1000*pi; % No. intervals for x
y0 = 0;
ym = pi; % Integral limits
m = 1000*pi; % No. intervals for y
hx = (xn - x0)/n; % x step size
hy = (ym - y0)/m; % y step size
I = 0;
for y = y0:hy:ym
A = 0;
for x = x0:hx:xn
A = A + hx*f(x,y);
A = A - 0.5*hx*(f(x0,y) + f(xn,y));
I = I + A*hy;
end
end

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回答（1 个）

Bjorn Gustavsson
Bjorn Gustavsson 2021-2-3
Use integral2 instead. That should solve this type of problem.
HTH

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