# How to solve or avoid the problem of “{log-affine} .* {concave}”?

Hi,I would like to achieve the following expression in CVX,where C_Rate and Ah are vectors(1400×1),R and Tbat are constants.We know exp() is convex,but x.^0.824 is concave.Therefore,It will prompt for errors in Matlab:
%Cannot perform the operation:
% {log-affine} .
{concave}
So is there any ways to solve or avoid this error in Matlab?Thanks to everyone for their help.

I mean how to implement this expression in CVX fitting DCP rule?

The FAQ adequately addresses your question. If you feel otherwise, do present your proof of convexity and we can help you show how that leads you to a DCP formulation.

All right,replace C_Rate with Ib/180 and Ah=Ib/3600.Bring two constant values R and Tbat.

make the second derivative of Ib,

ddQloss is negative at Ib belongs to[0,285], and [285,Inf] in positive.So does this prove that Qloss is a nonconvex problem when Ib belongs to[0,285]?Whatever it takes,thanks for your kind assistance.

Can you give me a reply?Thank you~:sweat:

hi brother ，have you solve this problem?