[stdlib_math] Add arange function.

doc/specs/stdlib_math.md

@@ -275,3 +275,61 @@ program demo_logspace_rstart_cbase
 
 end program demo_logspace_rstart_cbase
 ```
+## `seq` - Creates an vector of `integer/real` type with evenly spaced values within a given interval.
+
+### Status
+
+Experimental
+
+### Class
+
+Pure function.
+
+### Description
+
+Creates an vector of `integer/real` type with evenly spaced values within a given interval.
+
+### Syntax
+
+`result = [[stdlib_math(module):seq(interface)]](start [, end, by])`
+
+### Arguments
+
+`start`: Shall be an `integer/real` scalar.
+This is an `intent(in)` argument.
+
+`end`: Shall be an `integer/real` scalar.
+This is an `intent(in)` and `optional` argument.
+
+`by`: Shall be an `integer/real` scalar and large than `0`.
+This is an `intent(in)` and `optional` argument.  
+
+Warning:  
+If `by = 0`, the `by` argument will be corrected to `1/1.0` by the internal process of the `seq` function.   
+If `by < 0`, the `by` argument will be corrected to `abs(by)` by the internal process of the `seq` function. 
+
+### Return value
+
+Vector of evenly spaced values.
+
+For floating point arguments, the length of the result is `floor((end - start)/by) + 1`.
+
+### Example
+
+```fortran
+program demo_math_seq
+    use stdlib_math, only: seq
+
+    print *, seq(3)                 !! [1,2,3]
+    print *, seq(3.0)               !! [1.0,2.0,3.0]
+    print *, seq(-1)                !! [1,0,-1]
+    print *, seq(0,2)               !! [0,1,2]
+    print *, seq(1,-1)              !! [1,0,-1]
+    print *, seq(0, 2, 2)           !! [0,2]
+    print *, (1.0,1.0)*seq(3)       !! [(1.0,1.0),(2.0,2.0),[3.0,3.0]]
+
+    print *, seq(0.0,2.0,-2.0)      !! [0.0,2.0]. Not recommended: `by` argument is negative!
+    print *, seq(0.0,2.0,0.0)       !! [0.0,1.0]. Not recommended: `by` argument is zero!
+
+end program demo_math_seq
+```

src/CMakeLists.txt

@@ -32,6 +32,7 @@ set(fppFiles
     stdlib_math.fypp
     stdlib_math_linspace.fypp
     stdlib_math_logspace.fypp
+    stdlib_math_seq.fypp
     stdlib_string_type.fypp
 )
 

src/Makefile.manual

@@ -7,6 +7,7 @@ SRCFYPP =\
         stdlib_linalg.fypp \
         stdlib_linalg_diag.fypp \
         stdlib_linalg_outer_product.fypp \
+        stdlib_math_seq.fypp \
         stdlib_optval.fypp \
         stdlib_quadrature.fypp \
         stdlib_quadrature_trapz.fypp \
@@ -154,4 +155,7 @@ stdlib_math_linspace.o: \
 	stdlib_math.o
 stdlib_math_logspace.o: \
 	stdlib_math_linspace.o
+stdlib_math_seq.o: \
+    stdlib_math.o \
+    stdlib_kinds.o
 stdlib_linalg_outer_product.o: stdlib_linalg.o

src/stdlib_math.fypp

@@ -10,6 +10,7 @@ module stdlib_math
     public :: clip, linspace, logspace
     public :: EULERS_NUMBER_SP, EULERS_NUMBER_DP, EULERS_NUMBER_QP
     public :: DEFAULT_LINSPACE_LENGTH, DEFAULT_LOGSPACE_BASE, DEFAULT_LOGSPACE_LENGTH
+    public :: seq
 
     integer, parameter :: DEFAULT_LINSPACE_LENGTH = 100
     integer, parameter :: DEFAULT_LOGSPACE_LENGTH = 50
@@ -261,6 +262,21 @@ module stdlib_math
 
   end interface
 
+    !> Version: experimental
+    !>
+    !> `seq` creates an vector of `integer/real` type 
+    !>  with evenly spaced values within a given interval.
+    interface seq
+        #:set RI_KINDS_TYPES = REAL_KINDS_TYPES + INT_KINDS_TYPES
+        #:for k1, t1 in RI_KINDS_TYPES
+        pure module function seq_${t1[0]}$_${k1}$(start, end, by) result(result)
+            ${t1}$, intent(in) :: start
+            ${t1}$, intent(in), optional :: end, by
+            ${t1}$, allocatable :: result(:)
+        end function seq_${t1[0]}$_${k1}$
+        #:endfor
+    end interface seq
+
 contains
 
     #:for k1, t1 in IR_KINDS_TYPES

src/stdlib_math_seq.fypp

@@ -0,0 +1,58 @@
+#:include "common.fypp"
+submodule(stdlib_math) stdlib_math_seq
+
+    implicit none
+
+contains
+
+    #:for k1, t1 in REAL_KINDS_TYPES
+    !> `seq` creates an vector of `${t1}$` type 
+    !>  with evenly spaced values within a given interval.
+    pure module function seq_${t1[0]}$_${k1}$(start, end, by) result(result)
+
+        ${t1}$, intent(in) :: start
+        ${t1}$, intent(in), optional :: end, by
+        ${t1}$, allocatable :: result(:)
+
+        ${t1}$ :: start_, end_, by_
+        integer :: i
+
+        start_ = merge(start, 1.0_${k1}$, present(end))
+        end_   = merge(end,   start,      present(end))
+        by_    = sign(merge(merge(by, 1.0_${k1}$, by /= 0.0_${k1}$), &
+                 1.0_${k1}$, present(by)), end_ - start_)
+
+        allocate(result(floor((end_ - start_)/by_) + 1))
+            #!TODO: ??
+            #! floor or ceiling, floor is better.
+
+        result = [(start_ + (i - 1)*by_, i=1, size(result), 1)]
+
+    end function seq_${t1[0]}$_${k1}$
+    #:endfor
+
+    #:for k1, t1 in INT_KINDS_TYPES
+    !> `seq` creates an vector of `${t1}$` type 
+    !>  with evenly spaced values within a given interval.
+    pure module function seq_${t1[0]}$_${k1}$(start, end, by) result(result)
+
+        ${t1}$, intent(in) :: start
+        ${t1}$, intent(in), optional :: end, by
+        ${t1}$, allocatable :: result(:)
+
+        ${t1}$ :: start_, end_, by_
+        ${t1}$ :: i
+
+        start_ = merge(start, 1_${k1}$, present(end))
+        end_   = merge(end,   start,    present(end))
+        by_    = sign(merge(merge(by, 1_${k1}$, by /= 0_${k1}$), &
+                 1_${k1}$, present(by) ), end_ - start_)
+
+        allocate(result((end_ - start_)/by_ + 1))
+
+        result = [(i, i=start_, end_, by_)]
+
+    end function seq_${t1[0]}$_${k1}$
+    #:endfor
+
+end submodule stdlib_math_seq

src/tests/math/CMakeLists.txt

@@ -1,3 +1,4 @@
 ADDTEST(stdlib_math)
 ADDTEST(linspace)
-ADDTEST(logspace)
+ADDTEST(logspace)
+ADDTEST(math_seq)

src/tests/math/Makefile.manual

@@ -1,4 +1,5 @@
-PROGS_SRC = test_stdlib_math.f90 test_linspace.f90 test_logspace.f90
+PROGS_SRC = test_stdlib_math.f90 test_linspace.f90 test_logspace.f90 \
+    test_math_seq.f90
 
 
 include ../Makefile.manual.test.mk

src/tests/math/test_math_seq.f90

@@ -0,0 +1,53 @@
+!> SPDX-Identifier: MIT
+module test_math_seq
+
+    use stdlib_error, only: check
+    use stdlib_math, only: seq
+    implicit none
+
+    logical, private :: warn = .false.
+
+contains
+
+    subroutine test_math_seq_real
+        !> Normal
+        call check(all(seq(3.0) == [1.0, 2.0, 3.0]),        msg="all(seq(3.0) == [1.0,2.0,3.0]) failed.",           warn=warn)
+        call check(all(seq(-1.0) == [1.0, 0.0, -1.0]),      msg="all(seq(-1.0) == [1.0,0.0,-1.0]) failed.",         warn=warn)
+        call check(all(seq(0.0, 2.0) == [0.0, 1.0, 2.0]),   msg="all(seq(0.0,2.0) == [0.0,1.0,2.0]) failed.",       warn=warn)
+        call check(all(seq(1.0, -1.0) == [1.0, 0.0, -1.0]), msg="all(seq(1.0,-1.0) == [1.0,0.0,-1.0]) failed.",     warn=warn)
+        call check(all(seq(1.0, 1.0) == [1.0]),             msg="all(seq(1.0,1.0) == [1.0]) failed.",               warn=warn)
+        call check(all(seq(0.0, 2.0, 2.0) == [0.0, 2.0]),   msg="all(seq(0.0,2.0,2.0) == [0.0,2.0]) failed.",       warn=warn)
+        call check(all(seq(1.0, -1.0, 2.0) == [1.0, -1.0]), msg="all(seq(1.0,-1.0,2.0) == [1.0,-1.0]) failed.",     warn=warn)
+        !> Not recommended
+        call check(all(seq(0.0, 2.0, -2.0) == [0.0, 2.0]),  msg="all(seq(0.0,2.0,-2.0) == [0.0,2.0]) failed.",      warn=warn)
+        call check(all(seq(1.0, -1.0, -2.0) == [1.0, -1.0]),msg="all(seq(1.0,-1.0,-2.0) == [1.0,-1.0]) failed.",    warn=warn)
+        call check(all(seq(0.0, 2.0, 0.0) == [0.0,1.0,2.0]),msg="all(seq(0.0, 2.0, 0.0) == [0.0,1.0,2.0]) failed.", warn=warn)
+    end subroutine test_math_seq_real
+
+    subroutine test_math_seq_integer
+        !> Normal
+        call check(all(seq(3) == [1, 2, 3]),        msg="all(seq(3) == [1,2,3]) failed.",       warn=warn)
+        call check(all(seq(-1) == [1, 0, -1]),      msg="all(seq(-1) == [1,0,-1]) failed.",     warn=warn)
+        call check(all(seq(0, 2) == [0, 1, 2]),     msg="all(seq(0,2) == [0,1,2]) failed.",     warn=warn)
+        call check(all(seq(1, -1) == [1, 0, -1]),   msg="all(seq(1,-1) == [1,0,-1]) failed.",   warn=warn)
+        call check(all(seq(1, 1) == [1]),           msg="all(seq(1,1) == [1]) failed.",         warn=warn)
+        call check(all(seq(0, 2, 2) == [0, 2]),     msg="all(seq(0,2,2) == [0,2]) failed.",     warn=warn)
+        call check(all(seq(1, -1, 2) == [1, -1]),   msg="all(seq(1,-1,2) == [1,-1]) failed.",   warn=warn)
+        !> Not recommended
+        call check(all(seq(0, 2, -2) == [0, 2]),    msg="all(seq(0,2,-2) == [0,2]) failed.",    warn=warn)
+        call check(all(seq(1, -1, -2) == [1, -1]),  msg="all(seq(1,-1,-2) == [1,-1]) failed.",  warn=warn)
+        call check(all(seq(0, 2, 0) == [0,1,2]),    msg="all(seq(0, 2, 0) == [0,1,2]) failed.", warn=warn)
+    end subroutine test_math_seq_integer
+
+end module test_math_seq
+
+program tester
+
+    use test_math_seq
+
+    call test_math_seq_real
+    call test_math_seq_integer
+
+    print *, "All tests in `test_math_seq` passed."
+
+end program tester