Define log(2.0) as a constant.

Author: loiseaujc

src/stdlib_constants.fypp

@@ -71,6 +71,7 @@ module stdlib_constants
     #:for k, t, s in R_KINDS_TYPES
     ${t}$, parameter, public :: zero_${s}$ = 0._${k}$
     ${t}$, parameter, public :: one_${s}$  = 1._${k}$
+    ${t}$, parameter, public :: log2_${s}$ = log(2.0_${k}$)
     #:endfor
     #:for k, t, s in C_KINDS_TYPES
     ${t}$, parameter, public :: zero_${s}$ = (0._${k}$,0._${k}$)

src/stdlib_linalg_matrix_functions.fypp

@@ -30,7 +30,6 @@ contains
         real(${rk}$)        :: a_norm, c
         integer(ilp)        :: m, n, ee, k, s, order_, i, j
         logical(lk)         :: p
-        character(len=*), parameter :: this = "expm"
         type(linalg_state_type)     :: err0
 
         ! Deal with optional args.
@@ -54,7 +53,7 @@ contains
         a_norm = mnorm(A, "inf")
 
         ! Determine scaling factor for the matrix.
-        ee = int(log(a_norm) / log(2.0_${rk}$)) + 1
+        ee = int(log(a_norm) / log2_${rk}$) + 1
         s  = max(0, ee+1)
 
         ! Scale the input matrix & initialize polynomial.