Array arithmetic in bash

Question

I have number of arrays in bash, such as arrKey[], aarT[],P[] and I want to do an arithmetic operation with these arrays. As I checked, arrays are working perfectly but, the arithmetic to find array P[] is wrong. Can anyone help me with this, please?

    #The format is C[0] = (A[0,0]*B[0]) + (A[0,1]*B[1])

this is the code that I tried so far.

    P[0]= $(({arrKey[0,0]} * {arrT[0]} ))+ $(({arrKey[0,1]} * {arrT[1]})) ))
    echo ${P[0]}

Bash does not support multidimensional arrays. You can simulate it, like check this question for usage : stackoverflow.com/questions/16487258/… — Am_I_Helpful
– Am_I_Helpful, Commented Aug 21, 2016 at 14:36

user6717040 · Accepted Answer · 2016-08-21 15:40:09Z

There are several issues with your line of code:

P[0]= $(({arrKey[0,0]} * {arrT[0]} ))+ $(({arrKey[0,1]} * {arrT[1]})) ))

There is an additional space after the =, erase it.

P[0]=$(({arrKey[0,0]} * {arrT[0]} ))+ $(({arrKey[0,1]} * {arrT[1]})) ))

It is incorrect to add two elements outside of an Arithmetic expansion.
Remove the additional parentheses:
```
P[0]=$(({arrKey[0,0]} * {arrT[0]} + {arrKey[0,1]} * {arrT[1]}))
```
either use a $ or remove the {…} from variables inside a $(( … )):
```
P[0]=$(( arrKey[0,0] * arrT[0] + arrKey[0,1] * arrT[1] ))
```
Even if not strictly required, it is a good idea to quote your expansions:
```
P[0]="$(( arrKey[0,0] * arrT[0] + arrKey[0,1] * arrT[1] ))"
```

Also, make sure that the arrKey has been declared as an associative array:

declare -A arrKey

To make sure the intended double index 0,0 works.

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