llsq, a C++ code which solves the simple linear least squares (LLS) problem of finding the formula of a straight line y=a*x or y=a*x+b which minimizes the root-mean-square error to a set of N data points.


The computer code and data files described and made available on this web page are distributed under the MIT license


llsq is available in a C version and a C++ version and a FORTRAN90 version and a MATLAB version and a Python version.

Related Data and Programs:


MINPACK, a C++ code which solves systems of nonlinear equations, or the least squares minimization of the residual of a set of linear or nonlinear equations.

QR_SOLVE, a C++ code which computes the least squares solution of a linear system A*x=b.

TEST_APPROX, a C++ code which defines test problems for approximation, provided as a set of (x,y) data.

TEST_LLS, a C++ code which implements linear least squares test problems of the form A*x=b.


  1. David Kahaner, Cleve Moler, Steven Nash,
    Numerical Methods and Software,
    Prentice Hall, 1989,
    ISBN: 0-13-627258-4,
    LC: TA345.K34.

Source Code:

Last revised on 26 March 2020.