using for loop with syms

Question

Ashi Khajotia 2023-4-19

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1949613-using-for-loop-with-syms

评论： Ashi Khajotia 2023-4-19

Hello,

I would like to use for loop with syms,

So there a variable lam with which phi1 and phi2 will change and so do matrix M, now I want to use different M elements of each iteration in z. Can anyone help me in using For loop here?

syms n0 n1 n2 ns phi1 phi2
n0 = 1;
n1 = 2;
n2 = 1;
n3 = 2;
d1 = 0.1;
d2 = 0.2;
lam = 3:1:7;
th = 0;
phi1 =(d1./lam).*sqrt((n1));
phi2 = (d2./lam).*sqrt((n2));
for j = 1:length(lam)
    D0 = [2 2;  n0 -n0];
    D1 = [2 2;n1 -n1];
    D2 = [2 2; n2 -n2];
    D3 = [2 2;n3 -n3];
    P1 = [exp(-1i.*phi1) 1; 1 exp(1i.*phi1)];
    P2 = [exp(-1i*phi2) 1; 1 exp(1i*phi2)];
    M = D0*([D1*P1*D2*P2]^(2))*D3;
    Msubs = subs(M);
    Mvalue = double(Msubs);
    z = M(2,2)./M(1,1);
end
Error using *
Incorrect dimensions for matrix multiplication. Check that the number of columns in the first matrix matches the number of rows in the second matrix. To operate on each element of the matrix individually, use TIMES (.*) for elementwise multiplication.

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Askic V 2023-4-19

编辑：Askic V 2023-4-19

在 MATLAB Online 中打开

Hi Ashi,

first of all this line will produce an error:

% M = D0*([D1*P1*D2*P2]^(2))*D3;

Executing the whole script:

syms n0 n1 n2 ns phi1 phi2
n0 = 1;
n1 = 2;
n2 = 1;
n3 = 2;
d1 = 0.1;
d2 = 0.2;
lam = 3:1:7;
th = 0;
phi1 =(d1./lam).*sqrt((n1));
phi2 = (d2./lam).*sqrt((n2));
for j = 1:length(lam)
    D0 = [2 2;  n0 -n0];
    D1 = [2 2;n1 -n1];
    D2 = [2 2; n2 -n2];
    D3 = [2 2;n3 -n3];
    P1 = [exp(-1i.*phi1) 1; 1 exp(1i.*phi1)];
    P2 = [exp(-1i*phi2) 1; 1 exp(1i*phi2)];
    M = D0*([D1*P1*D2*P2]^(2))*D3;
    Msubs = subs(M);
    Mvalue = double(Msubs);
    z = M(2,2)./M(1,1);
end
Error using *
Incorrect dimensions for matrix multiplication. Check that the number of columns in the first matrix matches the number of rows in the second matrix. To operate on each element of the matrix individually, use TIMES (.*) for elementwise multiplication.

This is because D1*P1 is a matrix with dimensions 2x6, and D2 is a matrix of dimensions 2x2.

How Matrix M shuld look like? What is your intention here?

Just to be able to execute the line properly, you can do something like this:

M = D0*([D1*P1*(D2*P2)']^(2))*D3;

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Answer 1

Walter Roberson 2023-4-19

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1949613-using-for-loop-with-syms#answer_1218653

在 MATLAB Online 中打开

syms n0 n1 n2 ns phi1 phi2

n0 = 1;

n1 = 2;

n2 = 1;

n3 = 2;

d1 = 0.1;

d2 = 0.2;

lam = 3:1:7;

th = 0;

phi1 =(d1./lam).*sqrt((n1));

phi2 = (d2./lam).*sqrt((n2));

for j = 1:length(lam)

D0 = [2 2; n0 -n0];

D1 = [2 2;n1 -n1];

D2 = [2 2; n2 -n2];

D3 = [2 2;n3 -n3];

P1 = [exp(-1i.*phi1(j)) 1; 1 exp(1i.*phi1(j))];

P2 = [exp(-1i*phi2(j)) 1; 1 exp(1i*phi2(j))];

M = D0*([D1*P1*D2*P2]^(2))*D3;

Msubs = subs(M);

Mvalue = double(Msubs);

z(j,1) = M(2,2)./M(1,1);

end

plot(lam, real(z), lam, imag(z));

legend({'real', 'imaginary'})

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Dyuman Joshi 2023-4-19

在 MATLAB Online 中打开

I'm not sure why OP needs to use symbolic variables here

%syms n0 n1 n2 ns phi1 phi2

n0 = 1;

n1 = 2;

n2 = 1;

n3 = 2;

d1 = 0.1;

d2 = 0.2;

lam = 3:1:7;

th = 0;

phi1 =(d1./lam).*sqrt((n1));

phi2 = (d2./lam).*sqrt((n2));

z = zeros(size(lam));

for j = 1:numel(lam)

D0 = [2 2; n0 -n0];

D1 = [2 2;n1 -n1];

D2 = [2 2; n2 -n2];

D3 = [2 2;n3 -n3];

P1 = [exp(-1i.*phi1(j)) 1; 1 exp(1i.*phi1(j))];

P2 = [exp(-1i*phi2(j)) 1; 1 exp(1i*phi2(j))];

M = D0*([D1*P1*D2*P2]^(2))*D3;

z(j) = M(2,2)./M(1,1);

end

plot(lam, real(z), lam, imag(z));

legend({'real', 'imaginary'})

Ashi Khajotia 2023-4-19

OkkI just realised the answer. Thank you very much :D

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