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Re: [Help-gsl] angle between two vectors

From: John D Lamb
Subject: Re: [Help-gsl] angle between two vectors
Date: Sun, 28 Mar 2010 15:33:06 +0100

On Sun, 2010-03-28 at 11:07 +0200, Jordi wrote: 
> I am quite new to maths and gsl I would like to get the angle between two
> vectors.

In C it should be something like the following. (You may have to check
where acos is defined, check norm_u * norm_v != 0; and you may want a
direction with the angle.) For floats use snrm and sdot instead of dnrm
and ddot.

  gsl_vector* u, v;
  double norm_u, norm_v, x, angle;
  norm_u = gdl_blas_dnrm( u );
  norm_v = gdl_blas_dnrm( v );
  gsl_blas_ddot( u, v, &x );
  angle = acos( x / (norm_u * norm_v ) );


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