Function einsum_into 

pub fn einsum_into<'a, T: EinsumScalar>(
    notation: &str,
    operands: Vec<NdOperand<'_>>,
    output: &'a mut ArrayViewMutD<'a, T>,
    alpha: T,
    beta: T,
) -> Result<()>

Parse and evaluate an einsum expression, writing the result into a pre-allocated ndarray output with alpha/beta scaling.

output = alpha * einsum(operands) + beta * output