Dot product

Dot product
You are encouraged to solve this task according to the task description, using any language you may know.

Create a function/use an in-built function, to compute the dot product, also known as the scalar product of two vectors. If possible, make the vectors of arbitrary length.

As an example, compute the dot product of the vectors [1, 3, -5] and [4, -2, -1].

If implementing the dot product of two vectors directly, each vector must be the same length; multiply corresponding terms from each vector then sum the results to produce the answer.

Haskell

<lang haskell>dotp a b | length a == length b = sum (zipWith (*) a b)

        | otherwise = error "Vector sizes must match"

main = print $ dotp [1, 3, -5] [4, -2, -1] -- prints 3</lang>

J

<lang j> 1 3 _5 +/ . * 4 _2 _1 3

  dotp=: +/ . *    NB. define as a function
  1 3 _5  dotp 4 _2 _1

3</lang> Applies generally to matricies and arrays of higher dimensions and can be used with verbs/functions other than product and sum.

Logo

<lang logo>to dotprod :a :b

 output apply "sum (map "product :a :b)

end

show dotprod [1 3 -5] [4 -2 -1]  ; 3</lang>

Python

<lang python>def dotp(a,b):

   assert len(a) == len(b), 'Vector sizes must match'
   return sum(aterm * bterm for aterm,bterm in zip(a, b))

if __name__ == '__main__':

   a, b = [1, 3, -5], [4, -2, -1]
   assert dotp(a,b) == 3</lang>

Tcl

Library: tcllib

<lang tcl>package require math::linearalgebra

set a {1 3 -5} set b {4 -2 -1} set dotp [::math::linearalgebra::dotproduct $a $b] proc pp vec {return \[[join $vec ,]\]} puts "[pp $a] \u2219 [pp $b] = $dotp"</lang> Output:

[1,3,-5] ∙ [4,-2,-1] = 3.0