```
cvx_begin
```

variable X(4);

loss =1./(( pi*X.*X))

minimize(loss))

cvx_end

```
cvx_begin
```

variable X(4);

loss =1./(( pi*X.*X))

minimize(loss))

cvx_end

Your expression does not evaluate to a scalar. But that could easily be fixed.

More seriously `1/(x'*x)`

is neither convex nor concave when length(x) >= 2. For instance, the Hessian of `1/(x(1)^2+x(2)^2) `

has one negative and one positive eigenvalue at `x(1)=x(2)=1`

.

Any convexification of this would be a completely different model, which is not the purview of forum readers to formulate.

Note `1/x^2`

is convex for scalar `x`

, in which case `pow_p(x,-2)`

can be used.