add non-in-place subroutine example

Author: perazz

example/linalg/CMakeLists.txt

@@ -15,6 +15,7 @@ ADD_EXAMPLE(is_triangular)
 ADD_EXAMPLE(inverse1)
 ADD_EXAMPLE(inverse2)
 ADD_EXAMPLE(inverse3)
+ADD_EXAMPLE(inverse4)
 ADD_EXAMPLE(outer_product)
 ADD_EXAMPLE(trace)
 ADD_EXAMPLE(state1)

example/linalg/example_inverse4.f90

@@ -0,0 +1,22 @@
+! Matrix inversion example: subroutine interface
+program example_inverse4
+  use stdlib_linalg_constants, only: dp
+  use stdlib_linalg, only: invert,eye
+  implicit none
+
+  real(dp) :: A(2,2), Am1(2,2)
+
+  ! Input matrix (NB Fortran is column major! input columns then transpose)
+  A = transpose(reshape( [4, 3, &
+                          3, 2], [2,2] ))
+
+  ! Invert matrix
+  call invert(A,Am1)
+
+  print *, '         |',Am1(1,:),'|' ! | -2  3 |
+  print *, ' inv(A)= |',Am1(2,:),'|' ! |  3 -4 |
+
+  ! Final check 
+  print *, 'CHECK passed? ',matmul(A,Am1)==eye(2)
+
+end program example_inverse4