add tests

Author: cval26

test/test_fftpack_utils.f90

@@ -1,6 +1,6 @@
 module test_fftpack_utils
 
-    use fftpack, only: rk, fftshift, ifftshift
+    use fftpack, only: rk, fft, ifft, fftshift, ifftshift, fftfreq, rfftfreq
     use testdrive, only: new_unittest, unittest_type, error_type, check
     implicit none
     private
@@ -18,7 +18,11 @@ subroutine collect_utils(testsuite)
                     new_unittest("fftshift_complex", test_fftshift_complex), &
                     new_unittest("fftshift_real", test_fftshift_real), &
                     new_unittest("ifftshift_complex", test_fftshift_complex), &
-                    new_unittest("ifftshift_real", test_fftshift_real) &
+                    new_unittest("ifftshift_real", test_fftshift_real), &
+                    new_unittest("fftfreq_1", test_fftfreq_1), &
+                    new_unittest("fftfreq_2", test_fftfreq_2), &
+                    new_unittest("fftfreq_3", test_fftfreq_3), &
+                    new_unittest("rfftfreq", test_rfftfreq) &
                     ]
 
     end subroutine collect_utils
@@ -79,4 +83,78 @@ subroutine test_ifftshift_real(error)
 
     end subroutine test_ifftshift_real
 
+    subroutine test_fftfreq_1(error)
+        type(error_type), allocatable, intent(out) :: error
+        integer, dimension(8) :: target1 = [0, 1, 2, 3, -4, -3, -2, -1]
+        integer, dimension(9) :: target2 = [0, 1, 2, 3, 4, -4, -3, -2, -1]
+
+        call check(error, all(fftfreq(8) == target1),&
+                    "all(fftfreq(8) == target1) failed.")
+        if (allocated(error)) return
+        call check(error, all(fftfreq(9) == target2),&
+                    "all(fftfreq(9) == target2) failed.")
+    end subroutine test_fftfreq_1
+
+    subroutine test_fftfreq_2(error)
+        implicit none
+        type(error_type), allocatable, intent(out) :: error
+
+        real(rk), parameter :: tol = 1.0e-12_rk
+        real(rk), parameter :: twopi = 8*atan(1.0_rk)  !> 2*pi
+        complex(rk), parameter :: imu = (0,1)  !> imaginary unit
+
+        integer, parameter :: n = 128
+        integer :: i
+        complex(rk), dimension(n) :: xvec, xfou
+        real(rk), dimension(n) :: xtrue
+
+        do  i = 1, n
+            xvec(i) = cos(twopi*(i-1)/n)
+            xtrue(i) = -sin(twopi*(i-1)/n)  !> derivative in physical space
+        end do
+
+        xfou = fft(xvec)/n
+        xfou = imu*fftfreq(n)*xfou  !> derivative in Fourier space
+        xvec = ifft(xfou)
+        call check(error, maxval(abs(xvec-xtrue)) < tol, &
+                    "maxval(abs(xvec-xtrue)) < tol failed.")
+    end subroutine test_fftfreq_2
+
+    subroutine test_fftfreq_3(error)
+        implicit none
+        type(error_type), allocatable, intent(out) :: error
+
+        real(rk), parameter :: tol = 1.0e-12_rk
+        real(rk), parameter :: twopi = 8*atan(1.0_rk)  !> 2*pi
+        complex(rk), parameter :: imu = (0,1)  !> imaginary unit
+
+        integer, parameter :: n = 135
+        integer :: i
+        complex(rk), dimension(n) :: xvec, xfou
+        real(rk), dimension(n) :: xtrue
+
+        do  i = 1, n
+            xvec(i) = cos(twopi*(i-1)/n)
+            xtrue(i) = -sin(twopi*(i-1)/n)  !> derivative in physical space
+        end do
+
+        xfou = fft(xvec)/n
+        xfou = imu*fftfreq(n)*xfou  !> derivative in Fourier space
+        xvec = ifft(xfou)
+        call check(error, maxval(abs(xvec-xtrue)) < tol, &
+                    "maxval(abs(xvec-xtrue)) < tol failed.")
+    end subroutine test_fftfreq_3
+
+    subroutine test_rfftfreq(error)
+        type(error_type), allocatable, intent(out) :: error
+        integer, dimension(8) :: target1 = [0, 1, 1, 2, 2, 3, 3, -4]
+        integer, dimension(9) :: target2 = [0, 1, 1, 2, 2, 3, 3, 4, 4]
+
+        call check(error, all(rfftfreq(8) == target1),&
+                    "all(rfftfreq(8) == target1) failed.")
+        if (allocated(error)) return
+        call check(error, all(rfftfreq(9) == target2),&
+                    "all(rfftfreq(9) == target2) failed.")
+    end subroutine test_rfftfreq
+
 end module test_fftpack_utils