## Issue

I have written code using matmul, but I am getting the following error:

```
"ValueError: matmul: Input operand 1 has a mismatch in its core dimension 0, with gufunc signature (n?,k),(k,m?)->(n?,m?) (size 1 is different from 3)"
```

Code:

```
R = [[0.40348195], [0.38658295], [0.82931052]]
V = [0.33452744, 0.33823673, 0.32723583]
print("Rt_p: ", R)
B = np.matmul(V,np.transpose(R))/pow(LA.norm(R), 2)
print("B", B)
```

## Solution

You are transposing a Matrix with 3 rows and 1 column to a Matrix with 3 columns and 1 row.

Then you are multiplying it with a similar Matrix (also 3 columns 1 row) which is incorrect mathematically. So you can either remove the transpose function or define your R Matrix as 1 row 3 columns and then transpose it. Check this for further information.

Answered By – IcesHay

Answer Checked By – David Goodson (BugsFixing Volunteer)