calculus - Surface integration in MATLAB -


i'm facing problem in calculating surface integration. defined function below calculates surface integration discrete dataset using trapezoidal rule.

< trapz2d.m >  function out = trapz2d(x,y,f)     x = x(:);     y = y(:);     nx = length(x);     ny = length(y);      dx = diff(x);     dy = diff(y);     ds = dy*dx.';      df = (f(1:ny-1,1:nx - 1) + f(2:ny,1:nx-1) + f(1:ny-1,2:nx) + f(2:ny,2:nx))/4;     out = sum(sum(ds.*df)); end

i calculated surface integration using function , dataset in link below, , compare value obtained "trapz" matlab built-in function.

< surfinteg.m >  clc close clear format long load('dataset.mat')  i1 = trapz(y, trapz(x,pz3,2)); i2 = trapz2d(x,y,pz3); disp([i1; i2])  >>>1.0e-12 *    0.307618158054522 - 0.000000000004792i    0.307618158054522 - 0.000000000004792i  i1 = trapz(y, trapz(x,pz1,2)); i2 = trapz2d(x,y,pz1); disp([i1; i2])  >>>1.0e-27 *    -0.135645057561047 + 0.013248760976931i    -0.129284381233370 + 0.013497757971006i

the results similar "pz3", not "pz1". explain why happening?

dataset


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