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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _lincomb(self, a, x1, b, x2, out):
 """Implement the linear combination of ``x1`` and ``x2``. Compute ``out = a*x1 + b*x2`` using optimized BLAS routines if possible. This function is part of the subclassing API. Do not call it directly. Parameters a, b : `TensorSpace.field` element Scalars to multiply ``x1`` and ``x2`` with. x1, x2 : `NumpyTensor` Summands in the linear combination. out : `NumpyTensor` Tensor to which the result is written. Examples -------- rn(3).element([ 0., 1., 3.]) True """

        _lincomb_impl(a, x1, b, x2, out)