I get an error if I define |x|^4 this way. Am I doing something wrong?
pow_abs(pow_abs(x,2),2)
Error using cvx/pow_cvx (line 144)
Disciplined convex programming error:
Illegal operation: pow_abs( {convex}, {2} )
Error in cvx/pow_abs (line 13)
y = pow_cvx( x, p, ‘pow_abs’ );
Your outer pow_abs has an argument which is not affine. Hence the error.
help pow_abs
POW_POS Power of absolute value.
POW_POS(X,P) = ABS(X).^P.
P must be real and greater than or equal to one.Disciplined convex programming information: pow_abs(X,P) is convex and nonmonotonic, so X must be affine. P must be constant, and its elements must be greater than or equal to one. X may be complex.
Use
pow_abs(x,4)