Outer product

doc/specs/stdlib_linalg.md

@@ -168,3 +168,41 @@ program demo_trace
     print *, trace(A) ! 1 + 5 + 9
 end program demo_trace
 ```
+
+## `outer_product` - Computes the outer product of two vectors
+
+### Status
+
+Experimental
+
+### Description
+
+Computes the outer product of two vectors
+
+### Syntax
+
+`d = [[stdlib_linalg(module):outer_product(interface)]](u, v)`
+
+### Arguments
+
+`u`: Shall be a rank-1 array
+
+`v`: Shall be a rank-1 array
+
+### Return value
+
+Returns a rank-2 array equal to `u v^T` (where `u, v` are considered column vectors). The shape of the returned array is `[size(u), size(v)]`.
+
+### Example
+
+```fortran
+program demo_outer_product
+    use stdlib_linalg, only: outer_product
+    implicit none
+    real, allocatable :: A(:,:), u(:), v(:)
+    u = [1., 2., 3. ]
+    v = [3., 4.]
+    A = outer_product(u,v)
+    !A = reshape([3., 6., 9., 4., 8., 12.], [3,2])
+end program demo_outer_product
+```

src/CMakeLists.txt

@@ -9,6 +9,7 @@ set(fppFiles
     stdlib_io.fypp
     stdlib_linalg.fypp
     stdlib_linalg_diag.fypp
+    stdlib_linalg_outer_product.fypp
     stdlib_optval.fypp
     stdlib_sorting.fypp
     stdlib_sorting_ord_sort.fypp

src/Makefile.manual

@@ -6,6 +6,7 @@ SRCFYPP =\
         stdlib_io.fypp \
         stdlib_linalg.fypp \
         stdlib_linalg_diag.fypp \
+        stdlib_linalg_outer_product.fypp \
         stdlib_optval.fypp \
         stdlib_quadrature.fypp \
         stdlib_quadrature_trapz.fypp \
@@ -128,3 +129,4 @@ stdlib_stats_distribution_PRNG.o: \
 stdlib_string_type.o: stdlib_ascii.o stdlib_kinds.o
 stdlib_strings.o: stdlib_ascii.o stdlib_string_type.o
 stdlib_math.o: stdlib_kinds.o
+stdlib_linalg_outer_product.o: stdlib_linalg.o

src/stdlib_linalg.fypp

@@ -11,6 +11,7 @@ module stdlib_linalg
   public :: diag
   public :: eye
   public :: trace
+  public :: outer_product
 
   interface diag
     !! version: experimental
@@ -52,6 +53,7 @@ module stdlib_linalg
     #:endfor
   end interface
 
+
   ! Matrix trace
   interface trace
     !! version: experimental
@@ -63,6 +65,21 @@ module stdlib_linalg
     #:endfor
   end interface
 
+
+  ! Outer product (of two vectors)
+  interface outer_product
+    !! version: experimental
+    !!
+    !! Computes the outer product of two vectors, returning a rank-2 array
+    !! ([Specification](../page/specs/stdlib_linalg.html#description_3))
+    #:for k1, t1 in RCI_KINDS_TYPES
+      pure module function outer_product_${t1[0]}$${k1}$(u, v) result(res)
+        ${t1}$, intent(in) :: u(:), v(:)
+        ${t1}$ :: res(size(u),size(v))
+      end function outer_product_${t1[0]}$${k1}$
+    #:endfor
+  end interface outer_product
+
 contains
 
     function eye(n) result(res)

src/stdlib_linalg_outer_product.fypp

@@ -0,0 +1,20 @@
+#:include "common.fypp"
+#:set RCI_KINDS_TYPES = REAL_KINDS_TYPES + CMPLX_KINDS_TYPES + INT_KINDS_TYPES
+submodule (stdlib_linalg) stdlib_linalg_outer_product
+
+  implicit none
+
+contains
+
+  #:for k1, t1 in RCI_KINDS_TYPES
+    pure module function outer_product_${t1[0]}$${k1}$(u, v) result(res)
+      ${t1}$, intent(in) :: u(:), v(:)
+      ${t1}$ :: res(size(u),size(v))
+      integer :: col
+      do col = 1, size(v)
+        res(:,col) = v(col) * u
+      end do
+    end function outer_product_${t1[0]}$${k1}$
+  #:endfor
+
+end submodule