Re: Are scalars precomputed when multiplied with or added to vectors?

[David Bateman]

Olaf Till wrote:
> If x and y are vectors and all other variables are scalars, e.g. in
>
> octave:1> y = sqrt (x.^2 * a^2 + sqrt ((a + b)^2 + c * d)) + c + d;
>
> will all scalar subexpressions
>
> (i.e.: a^2, sqrt ((a + b)^2 + c * d), c + d)
>
> be computed by Octave only once for the operations on all components
> of x, or is it worth explicitly precomputing them?
>
>   
Given the precedence of the above the answer is yes for a^2 and
sqrt((a+b)^2+c*d). However for c + d the answer is less clear.. I
believe that the binop will treat this as two scalar/matrix additions
rather than a scalar/scalar addition and then a matrix/scalar addition..
Put parenthesis around c+d to ensure what you want.

D.

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