Array multiplication in codesys - arrays

Question

I wanted to multiply 2 matrices in codesys. I have implemented the code in the structured text language. However I am not able to generate the results correctly. Below is the logic which i am trying to implement.
Initialisation in codesys:
PROGRAM POU
VAR
a: ARRAY [1..5,1..2] OF INT:= [1,2,3,4,5,6,7,8,9,1];
b: ARRAY [1..2,1..5] OF INT := [1,2,3,4,5,6,7,8,9,1];
r1: INT:= 5; // no. of rows in a;
c1: INT:=2; // no. of columns in a;
r2: INT:= 2; //no. Of rows in b;
c2: INT:= 5; //no. of columns in b;
i: INT;
j: INT ;
k: INT;
z: INT:=2;
result: ARRAY [1..5,1..5] OF INT:= 0;
END_VAR
Program logic:
FOR i:=1 TO r1 DO
FOR j:=1 TO c2 DO
FOR k:=1 TO z DO
result[i,j]:= result[i,j]+(a[i,k]*b[k,j]);
END_FOR
END_FOR
END_FOR
What may be the reason for not getting the desired output?

Answer 1

The only obvious problem I see is, if you want to initialize an array with a specific value, don't do result: ARRAY [1..5, 1..5] OF INT := 0 as you would should get an error C0032: Cannot convert type 'BIT' to type 'ARRAY [1..5, 1..5] OF INT', instead do this: result: ARRAY [1..5, 1..5] OF INT := [ 25(0) ], although in codesys arrays Elements to which no initialization value is assigned explicitly are initialized internally with the default value of the basic data type, which in case of an INT is 0.
Also, to avoid errors, instad of hardcoding the boundaries I'd recomment to instad use the built in LOWER_BOUND an UPPER_BOUND functions.
Here's an example generic function for Matrix multiplication based on the code in your question:
METHOD IntMatrixProduct : BOOL
VAR_IN_OUT
A: ARRAY [*, *] OF INT;
B: ARRAY [*, *] OF INT;
C: ARRAY [*, *] OF INT;
END_VAR
VAR_INPUT
zero_C: BOOL := TRUE;
END_VAR
VAR
al1: DINT := LOWER_BOUND(A, 1);
au1: DINT := UPPER_BOUND(A, 1);
al2: DINT := LOWER_BOUND(A, 2);
au2: DINT := UPPER_BOUND(A, 2);
bl1: DINT := LOWER_BOUND(B, 1);
bu1: DINT := UPPER_BOUND(B, 1);
bl2: DINT := LOWER_BOUND(B, 2);
bu2: DINT := UPPER_BOUND(B, 2);
cl1: DINT := LOWER_BOUND(C, 1);
cu1: DINT := UPPER_BOUND(C, 1);
cl2: DINT := LOWER_BOUND(C, 2);
cu2: DINT := UPPER_BOUND(C, 2);
height: DINT := au1 - al1;
width: DINT := bu2 - bl2;
common: DINT := au2 - al2;
i, j, k: DINT;
END_VAR
IF (common <> bu1 - bl1 // Width of A != Height of B
OR_ELSE cu1 - cl1 <> height // Height of C != Height of A
OR_ELSE cu2 - cl2 <> width) THEN // Width of C != Width of B
IntMatrixProduct := FALSE; // Error!
RETURN;
END_IF
// Zero C
IF (zero_C) THEN
FOR i := 0 TO height DO
FOR j := 0 TO width DO
result[cl1 + i, cl2 + j] := 0;
END_FOR
END_FOR
END_IF
// Calcutale A*B
FOR i := 0 TO height DO
FOR j := 0 TO width DO
FOR k := 0 TO common DO
result[cl1 + i, cl2 + j] := result[cl1 + i, cl2 + j] + (a[al1 + i, al2 + k] * b[bl1 + k, bl2 + j]);
END_FOR
END_FOR
END_FOR
IntMatrixProduct := TRUE; // Success
You can also try importing the code using PLCOpen from here.
PS. Here's the result I get after running the above function: