[Octave-bug-tracker] [bug #66652] Element power operator causes numerical error but only if broadcasting vector

[anonymous]

URL:
  <https://savannah.gnu.org/bugs/?66652>

                 Summary: Element power operator causes numerical error but
only if broadcasting vector
                   Group: GNU Octave
               Submitter: None
               Submitted: Fri 10 Jan 2025 04:39:20 PM UTC
                Category: Octave Function
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Incorrect Result
                  Status: None
             Assigned to: None
         Originator Name:
        Originator Email:
             Open/Closed: Open
         Discussion Lock: Any
                 Release: 9.3.0
        Operating System: GNU/Linux
           Fixed Release: None
         Planned Release: None


    _______________________________________________________

Follow-up Comments:


-------------------------------------------------------
Date: Fri 10 Jan 2025 04:39:20 PM UTC By: Anonymous
Broadcasting with element power operator causes small but unnecessary
numerical error.

Problem is only with broadcasting different sizes, not scalar or equal size
matrix.


# exponent vector
p = [2 1 0]

# scalar .^ vector is correct
x = i .^ p, x - round(x)
x = (2i) .^ p, x - round(x)
x = (3i) .^ p, x - round(x)

# column vector .^ row vector has numerical error
x = [i; 2i; 3i] .^ p, x - round(x)

# expanding vectors to full matrix is correct again
x = [i i i; 2i 2i 2i; 3i 3i 3i] .^ [2 1 0; 2 1 0; 2 1 0]
x - round (x)


Full matrix result:

>> x = [i i i; 2i 2i 2i; 3i 3i 3i] .^ [2 1 0; 2 1 0; 2 1 0], x - round (x)
x =
  -1 + 0i   0 + 1i   1 + 0i
  -4 + 0i   0 + 2i   1 + 0i
  -9 + 0i   0 + 3i   1 + 0i

ans =
   0   0   0
   0   0   0
   0   0   0


Vector broadcast error result:

>> x = [i; 2i; 3i] .^ [2 1 0], x - round (x)
x =
  -1.0000 + 0.0000i   0.0000 + 1.0000i   1.0000 +      0i
  -4.0000 + 0.0000i   0.0000 + 2.0000i   1.0000 +      0i
  -9.0000 + 0.0000i   0.0000 + 3.0000i   1.0000 +      0i

ans =
            0 + 1.2246e-16i   6.1232e-17 +          0i            0 +
0i
            0 + 4.8986e-16i   1.2246e-16 +          0i            0 +
0i
  -1.7764e-15 + 1.1022e-15i   1.8370e-16 + 4.4409e-16i            0 +
0i









    _______________________________________________________

Reply to this item at:

  <https://savannah.gnu.org/bugs/?66652>

_______________________________________________
Message sent via Savannah
https://savannah.gnu.org/

signature.asc
Description: PGP signature