operator(.inv.): return NaNs on exceptions

Author: perazz

doc/specs/stdlib_linalg.md

@@ -1015,7 +1015,8 @@ This interface is equivalent to the function version of  [[stdlib_linalg(module)
 
 Returns a rank-2 square array with the same type, kind and rank as `a`, that contains the inverse of `a`.
 
-Exceptions always trigger an `error stop`.
+If an exception occurred on input errors, or singular matrix, NaNs will be returned.
+
 
 ### Example
 

src/stdlib_linalg.fypp

@@ -655,7 +655,8 @@ module stdlib_linalg
     !!### Description
     !! 
     !! This operator interface provides a convenient way to compute the inverse of a matrix.
-    !! Supported data types include `real` and `complex`.
+    !! Supported data types include `real` and `complex`. On input errors or singular matrix, 
+    !! NaNs will be returned.
     !!
     !!@note The provided functions are intended for square matrices.
     !!@note BLAS/LAPACK backends do not currently support extended precision (``xdp``).

src/stdlib_linalg_inverse.fypp

@@ -6,6 +6,7 @@ submodule (stdlib_linalg) stdlib_linalg_inverse
      use stdlib_linalg_lapack, only: getri,getrf,stdlib_ilaenv
      use stdlib_linalg_state, only: linalg_state_type, linalg_error_handling, LINALG_ERROR, &
          LINALG_INTERNAL_ERROR, LINALG_VALUE_ERROR
+     use ieee_arithmetic, only: ieee_value, ieee_quiet_nan
      implicit none(type,external)
 
      character(*), parameter :: this = 'inverse'  
@@ -153,9 +154,17 @@ submodule (stdlib_linalg) stdlib_linalg_inverse
          ${rt}$, intent(in) :: a(:,:)
          !> Result matrix
          ${rt}$, allocatable :: inva(:,:)
+         
+         type(linalg_state_type) :: err
 
-         ! Do not provide an error handler (error stop on issues)
-         inva = stdlib_linalg_inverse_${ri}$(a)
+         ! Provide an error handler to return NaNs on issues
+         inva = stdlib_linalg_inverse_${ri}$(a,err=err)
+         
+         ! Return NaN on issues
+         if (err%error()) then 
+            if (allocated(inva)) deallocate(inva)
+            allocate(inva(size(a,1,kind=ilp),size(a,2,kind=ilp)),source=ieee_value(1.0_${rk}$,ieee_quiet_nan))
+         endif
 
      end function stdlib_linalg_inverse_${ri}$_operator