Add procedure to create a complex imaginary tensor from a real tensor

src/arraymancer/tensor/complex.nim

@@ -43,6 +43,21 @@ proc complex*[T: SomeNumber](re: Tensor[T]): auto {.inline, noinit.} =
   else:
     map_inline(re, complex(x))
 
+proc complex_imag*[T: SomeNumber](im: Tensor[T]): auto {.inline, noinit.} =
+  ## Create a new, imaginary Tensor from a single real Tensor
+  ##
+  ## The input Tensor is copied into the imaginary part of the output Tensor,
+  ## while the real part is set to all zeros.
+  ##
+  ## If the input is an integer Tensor, the output will be a Tensor of
+  ## Complex64 to avoid any loss of precision. If you want to convert it
+  ## into a Tensor of Complex32, you must convert the input to float32 first
+  ## by using `.asType(float32)`.
+  when T is SomeInteger:
+    map_inline(im, complex(float64(0.0), float64(x)))
+  else:
+    map_inline(im, complex(T(0.0), x))
+
 proc real*[T: SomeFloat](t: Tensor[Complex[T]]): Tensor[T] {.inline, noinit.} =
   ## Get the real part of a complex Tensor (as a float Tensor)
   t.map_inline(x.re)

tests/tensor/test_complex.nim

@@ -56,6 +56,24 @@ proc main() =
         check: c64_from_int == expected_c64
         check: c32 == expected_c32
 
+      block: # Single tensor to imaginary complex conversion
+        var im_int = [1, -10, 20].toTensor
+        var im_float64 = im_int.asType(float64)
+        var im_float32 = im_int.asType(float32)
+        var c64_imag_from_int = complex_imag(im_int)
+        var c64_imag = complex_imag(im_float64)
+        var c32_imag = complex_imag(im_float32)
+        var expected_imag64 = [complex64(0.0, 1.0),
+                               complex64(0.0, -10.0),
+                               complex64(0.0, 20.0)].toTensor
+        var expected_imag32 = [complex32(0.0, 1.0),
+                               complex32(0.0, -10.0),
+                               complex32(0.0, 20.0)].toTensor
+
+        check: c64_imag == expected_imag64
+        check: c64_imag_from_int == expected_imag64
+        check: c32_imag == expected_imag32
+
     test "Get the Real and Imaginary Components of a Complex Tensor":
       var c = [
         complex(1.0, -300.0),