calculate integration of function

Question

MADHVI 2023-8-13

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2008007-calculate-integration-of-function

评论： Star Strider 2023-8-14

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)

1 个评论
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Dyuman Joshi 2023-8-13

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.

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Answer 1

Star Strider 2023-8-13

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2008007-calculate-integration-of-function#answer_1287022

在 MATLAB Online 中打开

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

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 =