Function rgsl::fit::wmul

pub fn wmul(
    x: &[f64],
    xstride: usize,
    w: &[f64],
    wstride: usize,
    y: &[f64],
    ystride: usize,
    n: usize
) -> Result<(f64, f64, f64), Value>

Returns (c1, cov11, sumsq).