Conversion functions from degrees to radians and vice-versa.

doc/specs/stdlib_math.md

@@ -382,6 +382,70 @@ Notes: Although the angle of the complex number `0` is undefined, `argpi((0,0))`
 {!example/math/example_math_argpi.f90!}
 ```
 
+### `deg2rad`
+
+#### Status
+
+Experimental
+
+#### Class
+
+Elemenal function.
+
+### Description
+
+`deg2rad` converts phase angles from degrees to radians.
+
+#### Syntax
+
+`result = ` [[stdlib_math(module):deg2rad(interface)]] `(theta)`
+
+#### Arguments
+
+`theta`: Shall be a `real` scalar/array.
+
+#### Return value
+
+Returns the `real` phase angle in radians.
+
+#### Example
+
+```fortran
+{!example/math/example_math_deg2rad.f90!}
+```
+
+### `rad2deg`
+
+#### Status
+
+Experimental
+
+#### Class
+
+Elemenal function.
+
+### Description
+
+`rad2deg` converts phase angles from radians to degrees.
+
+#### Syntax
+
+`result = ` [[stdlib_math(module):rad2deg(interface)]] `(theta)`
+
+#### Arguments
+
+`theta`: Shall be a `real` scalar/array.
+
+#### Return value
+
+Returns the `real` phase angle in degrees.
+
+#### Example
+
+```fortran
+{!example/math/example_math_rad2deg.f90!}
+```
+
 ### `is_close` function
 
 #### Description

example/math/CMakeLists.txt

@@ -12,5 +12,7 @@ ADD_EXAMPLE(math_arange)
 ADD_EXAMPLE(math_argd)
 ADD_EXAMPLE(math_arg)
 ADD_EXAMPLE(math_argpi)
+ADD_EXAMPLE(math_deg2rad)
+ADD_EXAMPLE(math_rad2deg)
 ADD_EXAMPLE(math_is_close)
 ADD_EXAMPLE(meshgrid)

example/math/example_math_deg2rad.f90

@@ -0,0 +1,8 @@
+program example_math_deg2rad
+    use stdlib_math, only: deg2rad
+    implicit none
+    print *, deg2rad(0.0)       ! 0.0
+    print *, deg2rad(90.0)      ! 1.57508
+    print *, deg2rad(-180.0)    ! -3.1416
+
+end program example_math_deg2rad

example/math/example_math_rad2deg.f90

@@ -0,0 +1,9 @@
+program example_math_rad2deg
+    use stdlib_math, only: rad2deg
+    use stdlib_constants, only: PI_sp
+    implicit none
+    print *, rad2deg(0.0)              ! 0.0
+    print *, rad2deg(PI_sp / 2.0)      ! 90.0
+    print *, rad2deg(-PI_sp)           ! -3.1416
+
+end program example_math_rad2deg

src/stdlib_math.fypp

@@ -15,7 +15,7 @@ module stdlib_math
 #:endif
     public :: DEFAULT_LINSPACE_LENGTH, DEFAULT_LOGSPACE_BASE, DEFAULT_LOGSPACE_LENGTH
     public :: stdlib_meshgrid_ij, stdlib_meshgrid_xy
-    public :: arange, arg, argd, argpi, is_close, all_close, diff, meshgrid
+    public :: arange, arg, argd, argpi, deg2rad, rad2deg, is_close, all_close, diff, meshgrid
 
     integer, parameter :: DEFAULT_LINSPACE_LENGTH = 100
     integer, parameter :: DEFAULT_LOGSPACE_LENGTH = 50
@@ -332,6 +332,26 @@ module stdlib_math
         procedure :: argpi_${k1}$
         #:endfor
     end interface argpi
+
+    !> Version: experimental
+    !> 
+    !> `deg2rad` converts phase angles from degrees to radians.
+    !> ([Specification](../page/specs/stdlib_math.html#deg2rad-function))
+    interface deg2rad
+        #:for k1 in REAL_KINDS
+        procedure :: deg2rad_${k1}$
+        #:endfor
+    end interface deg2rad
+
+    !> Version: experimental
+    !> 
+    !> `rad2deg` converts phase angles from radians to degrees.
+    !> ([Specification](../page/specs/stdlib_math.html#rad2deg-function))
+    interface rad2deg
+        #:for k1 in REAL_KINDS
+        procedure :: rad2deg_${k1}$
+        #:endfor
+    end interface rad2deg
 
     !> Returns a boolean scalar/array where two scalar/arrays are element-wise equal within a tolerance.
     !> ([Specification](../page/specs/stdlib_math.html#is_close-function))
@@ -453,6 +473,22 @@ contains
     end function argpi_${k1}$
     #:endfor
 
+    #:for k1, t1 in REAL_KINDS_TYPES
+    elemental function deg2rad_${k1}$(theta) result(result)
+        ${t1}$, intent(in) :: theta
+        ${t1}$ :: result
+        result = theta * PI_${k1}$ / 180.0_${k1}$
+
+    end function deg2rad_${k1}$
+
+    elemental function rad2deg_${k1}$(theta) result(result)
+        ${t1}$, intent(in) :: theta
+        ${t1}$ :: result
+        result = theta * 180.0_${k1}$ / PI_${k1}$
+
+    end function rad2deg_${k1}$
+    #:endfor
+
     #:for k1, t1 in INT_KINDS_TYPES
     !> Returns the greatest common divisor of two integers of kind ${k1}$
     !> using the Euclidean algorithm.

test/math/test_stdlib_math.fypp

@@ -5,7 +5,7 @@
 module test_stdlib_math
     use testdrive, only : new_unittest, unittest_type, error_type, check, skip_test
     use stdlib_math, only: clip, arg, argd, argpi, arange, is_close, all_close, diff, &
-                           arange
+                           arange, deg2rad, rad2deg
     use stdlib_kinds, only: int8, int16, int32, int64, sp, dp, xdp, qp
     implicit none
 
@@ -45,6 +45,12 @@ contains
             , new_unittest("argpi-cmplx-${k1}$", test_argpi_${k1}$) &
             #:endfor
 
+            !> Tests for deg2rad/rad2deg
+            #:for k1 in REAL_KINDS
+            , new_unittest("deg2rad-real-${k1}$", test_deg2rad_${k1}$) &
+            , new_unittest("rad2deg-real-${k1}$", test_rad2deg_${k1}$) &
+            #:endfor
+
             !> Tests for `is_close` and `all_close`
             #:for k1 in REAL_KINDS
             , new_unittest("is_close-real-${k1}$", test_is_close_real_${k1}$) &
@@ -301,6 +307,26 @@ contains
 
     end subroutine test_argpi_${k1}$
     #:endfor
+
+    #:for k1 in REAL_KINDS
+    subroutine test_deg2rad_${k1}$(error)
+        type(error_type), allocatable, intent(out) :: error
+        real(${k1}$), parameter :: tol = sqrt(epsilon(1.0_${k1}$))
+
+        call check(error, PI_${k1}$, deg2rad(180.0_${k1}$), thr=tol)
+        if (allocated(error)) return
+
+    end subroutine test_deg2rad_${k1}$
+
+    subroutine test_rad2deg_${k1}$(error)
+        type(error_type), allocatable, intent(out) :: error
+        real(${k1}$), parameter :: tol = sqrt(epsilon(1.0_${k1}$))
+
+        call check(error, 180.0_${k1}$, rad2deg(PI_${k1}$), thr=tol)
+        if (allocated(error)) return
+
+    end subroutine test_rad2deg_${k1}$
+    #:endfor
 
     #:for k1 in REAL_KINDS
     subroutine test_is_close_real_${k1}$(error)