Fix sturmLiouvilleLegendre bug

[jbrzensk]

What type of PR is this? (check all applicable)

• Refactor
• Feature
• Bug Fix
• Optimization
• Example
• Documentation

Description

Fixes sturmLiouvilleLegendre to match MATLAB, error matches MATLAB implementations.
Before fix:

norm(u_numerical) = 1.42275
norm(u_exact) = 2.1814
norm(u_numerical - u_exact) = 1.56892

After fix:

examples/cpp/sturmLiouvilleLegendre 
norm(u_numerical) = 2.17386
norm(u_exact) = 2.1814
norm(u_numerical - u_exact) = 0.0162423

Related Issues & Documents

• Closes C++ sturmLiouvilleLegendre has a bug #258

Added/updated tests?

• Yes
• No, and this is why: existing tests suffice
• I need help with writing tests

Read Contributing Guide and Code of Conduct

• I have read and followed the Contributing Guide and the Code of Conduct

[jbrzensk]

It’s the coefficient of that term. It has no special meaning, other than what the equations simplify to. Like the 2.0 in the previous term, just a coefficient of the scheme. Don’t know what it was turned into n*(n+1)??

…

On Mon, Dec 22, 2025 at 2:02 PM Angel Boada ***@***.***> wrote: ***@***.**** commented on this pull request. ------------------------------ In examples/cpp/sturmLiouvilleLegendre.cpp <#265 (comment)>: > @@ -57,7 +57,7 @@ int main() // Set up system of equations arma::sp_mat xc_mat = arma::sp_mat( arma::diagmat(xc) ); // x arma::sp_mat xc_mat_sq = arma::sp_mat( arma::diagmat(1 - arma::pow(xc, 2)) ); // 1 - x^2 - arma::sp_mat A = xc_mat_sq * (arma::sp_mat)L - 2 * xc_mat * (arma::sp_mat)I * (arma::sp_mat)G + n * (n-1) * arma::speye(m+2, m+2); + arma::sp_mat A = xc_mat_sq * (arma::sp_mat)L - 2.0 * xc_mat * (arma::sp_mat)I * (arma::sp_mat)G + (12.0 * arma::speye(m+2, m+2)); What is this 12.0? Could we benefit from a named constant? — Reply to this email directly, view it on GitHub <#265 (review)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AA7CSHKWF6MF4PIPE2OEZZD4DBTATAVCNFSM6AAAAACPOYLAKKVHI2DSMVQWIX3LMV43YUDVNRWFEZLROVSXG5CSMV3GSZLXHMZTMMBVHA4TEMJZGY> . You are receiving this because you were assigned.Message ID: ***@***.***>