calculate integration of function

clc
clear
syms x y z D L B A(m, n, j, t) R
nfin = 1; nffin = 3;     % length of summation of n
jfin = 1; jffin = 3;     % length of summation of j
mfin = 1; mffin = 3;     % length of summation of m
rowmat = [0];
for kk1=nfin:nffin
    for kk2 = jfin:jffin
        for kk3 = mfin:mffin
            rownew = A(kk1, kk2, kk3, t)*sin(kk1*pi*x)*cos(kk2*pi*D*y/L)*cos(kk3*D*pi*z/B); 
            rowmat = [rowmat rownew]; 
        end
    end
end
Phiterms = rowmat(2:end);  
Phi = sum(Phiterms.')
size(Phiterms)
diff(Phi,y,2)+diff(Phi,z,2)),t,1)+diff(diff(Phi,y,1),x,1)*(diff(diff(Phi,y,1),x,2)+diff(diff(Phi,y,1),y,2)+diff(diff(Phi,y,1),z,2))+diff(diff(Phi,z,1),x,1)*(diff(diff(Phi,z,1),x,2)+diff(diff(Phi,z,1),y,2)+diff(diff(Phi,z,1),z,2))-(diff(Phi,y,2)+diff(Phi,z,2))*(R+(diff(diff(Phi,x,1),x,2)+diff(diff(Phi,x,1),y,2)+diff(diff(Phi,x,1),z,2)))==diff(Phi,x,4)+diff(Phi,y,4)+diff(Phi,z,4)

Invalid expression. When calling a function or indexing a variable, use parentheses. Otherwise, check for mismatched delimiters.

colmat=[];

for kk1=nfin:nffin
    for kk2=mfin:mffin
        for kk3=jfin:jffin
            colnew1 = int(ans*sin(kk1*pi*x), 0, 1);
            colnew2 = int(colnew1*cos(kk2*pi*y*D/L), 0, L/D);
            colnew3 = int(colnew2*cos(kk3*pi*z*D/B), 0, B/D);
            colmat = [colmat; colnew3];
        end
    end
end

Phi_terms = colmat(2:end);
Phi_ = sum(Phi_terms);
size(Phi_terms)

[Dyuman Joshi]

You have undefined variables in your code - m, n, j, and t.

Also, please explain what you are doing here, what is the objective and what error/problem you are facing.

Answer 1

[Star Strider]

This term, near the beginning of what I call ‘EXPR’

diff(Phi,y,2)+diff(Phi,z,2),t,1)+ ...

needs an extra diff call:

diff(Phi,y,2)+diff(diff(Phi,z,2),t,1)+ ...

then it works.

Beyond that, it’s not obvious what this code does, however with that change (even though you do not appear to do anything with that value) the code runs without error —

syms x y z D L B A(m, n, j, t) R
nfin = 1; nffin = 3;     % length of summation of n
jfin = 1; jffin = 3;     % length of summation of j
mfin = 1; mffin = 3;     % length of summation of m
rowmat = [0];
    for kk1=nfin:nffin
        for kk2 = jfin:jffin
            for kk3 = mfin:mffin
        rownew = A(kk1, kk2, kk3, t)*sin(kk1*pi*x)*cos(kk2*pi*D*y/L)*cos(kk3*D*pi*z/B); 
        rowmat = [rowmat rownew]; 
            end
        end
    end
Phiterms = rowmat(2:end);  
Phi = sum(Phiterms.')

Phi = 

size(Phiterms)

ans = 1×2

1 27

EXPR = diff(Phi,y,2)+diff(diff(Phi,z,2),t,1)+diff(diff(Phi,y,1),x,1)*(diff(diff(Phi,y,1),x,2)+diff(diff(Phi,y,1),y,2)+diff(diff(Phi,y,1),z,2))+diff(diff(Phi,z,1),x,1)*(diff(diff(Phi,z,1),x,2)+diff(diff(Phi,z,1),y,2)+diff(diff(Phi,z,1),z,2))-(diff(Phi,y,2)+diff(Phi,z,2))*(R+(diff(diff(Phi,x,1),x,2)+diff(diff(Phi,x,1),y,2)+diff(diff(Phi,x,1),z,2)))==diff(Phi,x,4)+diff(Phi,y,4)+diff(Phi,z,4)

EXPR = 

colmat=[];
 
 for kk1=nfin:nffin
    for kk2=mfin:mffin
      for kk3=jfin:jffin
     colnew1 = int(ans*sin(kk1*pi*x), 0, 1);
     colnew2 = int(colnew1*cos(kk2*pi*y*D/L), 0, L/D);
     colnew3 = int(colnew2*cos(kk3*pi*z*D/B), 0, B/D);
     colmat = [colmat; colnew3];
  end
  end
 end
 
Phi_terms = colmat(2:end);
Phi_ = sum(Phi_terms);
size(Phi_terms)

ans = 1×2

1 53

.

[MADHVI]

Thanks.

[Star Strider]

My pleasure!

If my Answer helped you solve your problem, please Accept it!

.