How do I return something only if all steps of an conditional statement is true?

I am attempting to generate a random 4x4 matrix and if all the real parts of the eigenvalues are negative, then compute the inverse matrix of the original random matrix.

m=4;
G=randn(m);
H=eig(G);
J=real(H);
[rowsJ,colsJ]=size(J);
for r=1:rowsJ
    if J(r,1)<1
        K=G^-1
else
    printf("Unable to Compute")
    end
end

[John D'Errico]

If all the real parts are true? What could that mean to you? What do you mean by true?

[Allison Bushman]

Sorry, I meant "if all real parts are negative"

[Walter Roberson]

You should be testing J<0 rather than J<1 if you want negative.

[John D'Errico]

Oh, then the test is just

all(real(eig) < 0)

Answer 1

[Walter Roberson]

if all(J(:)<1)
    K=inv(G);
else
    K = [];
    printf("Unable to Compute")
end

However... you should rarely be computing the inverse of a matrix. In most cases you should be using other approaches than inv(), such as using the \ operator.

[Allison Bushman]

Thank you, but why should I not be computing the inverse of a matrix?

[Walter Roberson]

What do you do with K once you have computed it? Chances are high that you proceed to multiply it by something or multiply something by it, A*K or K*B . Instead of computing K=inv(G) and A*K you would compute A/G . Instead of computing K=inv(G) and K*B you would compute G\B

[Allison Bushman]

Okay. Thank you

[Stephen23]

"but why should I not be computing the inverse of a matrix?"

inv is slower and less accurate than the recommended methods of solving systems of linear equations.

The inv documentation explains: "It is seldom necessary to form the explicit inverse of a matrix. A frequent misuse of inv arises when solving the system of linear equations Ax = b. One way to solve the equation is with x = inv(A)*b. A better way, from the standpoint of both execution time and numerical accuracy, is to use the matrix backslash operator x = A\b."