code: def multiply(a, col):
      
      a = a.reshape(4, 4, 4)
      col = col.reshape(4, 8)
      return fcat(
          rowxcol(a[0], col),
          rowxcol(a[1], col),
          rowxcol(a[2], col),
          rowxcol(a[3], col),
      )
docs: Multiply a matrix by one column.