Did you read the Users’ Guide entry for inv_pos, or better yet the help?

help inv_pos

inv_pos Reciprocal of a positive quantity.
inv_pos(X) returns 1./X if X is positive, and +Inf otherwise.
X must be real.

For matrices and N-D arrays, the function is applied to each element.
Disciplined convex programming information:
inv_pos is convex and nonincreasing; therefore, when used in CVX
specifications, its argument must be concave (or affine).

Correct use of inv_pos presumes new_R is elementwise nonnegative. if it is not, the problem is not convex.

Thank you for your reply, another question please, is the cvx takes too much time to solve problem, because i have ran my code an hour ago until now it does not finish, knowning that i used a large matrix and when i do pause, I notice that other files are appearing like: inv_pos,pow_cvx,geo_mean_cone,eq,cvx_classify,cvx_vexity. What does mean?