{"record":{"id":"0bcf5c5032811816","repo":"Yalantis/uCrop","slug":"solve-lapack-library-function-sgels-returned","errorCode":null,"errorMessage":"solve(): LAPACK library function sgels() returned error code %d.","messagePattern":"solve\\(\\): LAPACK library function sgels\\(\\) returned error code (.+?)\\.","errorType":"console","errorClass":null,"httpStatus":null,"severity":"warning","filePath":"ucrop/src/main/jni/CImg.h","lineNumber":33058,"sourceCode":"        res.move_to(*this);\n#endif\n      } else { // Least-square solution for non-square systems\n\n#ifdef cimg_use_lapack\n        char TRANS = 'N';\n        int INFO, N = A._width, M = A._height, LWORK = -1, LDA = M, LDB = M, NRHS = _width;\n        Ttfloat WORK_QUERY;\n        Ttfloat\n          * const lapA = new Ttfloat[M*N],\n          * const lapB = new Ttfloat[M*NRHS];\n        cimg::sgels(TRANS, M, N, NRHS, lapA, LDA, lapB, LDB, &WORK_QUERY, LWORK, INFO);\n        LWORK = (int) WORK_QUERY;\n        Ttfloat *const WORK = new Ttfloat[LWORK];\n        cimg_forXY(A,k,l) lapA[k*M + l] = (Ttfloat)(A(k,l));\n        cimg_forXY(*this,k,l) lapB[k*M + l] = (Ttfloat)((*this)(k,l));\n        cimg::sgels(TRANS, M, N, NRHS, lapA, LDA, lapB, LDB, WORK, LWORK, INFO);\n        if (INFO!=0)\n          cimg::warn(_cimg_instance\n                     \"solve(): LAPACK library function sgels() returned error code %d.\",\n                     cimg_instance,\n                     INFO);\n        assign(NRHS, N);\n        if (!INFO) cimg_forXY(*this,k,l) (*this)(k,l) = (T)lapB[k*M + l];\n        else (A.get_invert(use_LU)*(*this)).move_to(*this);\n        delete[] lapA; delete[] lapB; delete[] WORK;\n#else\n        (A.get_invert(use_LU)*(*this)).move_to(*this);\n#endif\n      }\n      return *this;\n    }\n\n    //! Solve a system of linear equations \\newinstance.\n    template<typename t>\n    CImg<_cimg_Ttfloat> get_solve(const CImg<t>& A, const bool use_LU=false) const {\n      typedef _cimg_Ttfloat Ttfloat;","sourceCodeStart":33040,"sourceCodeEnd":33076,"githubUrl":"https://github.com/Yalantis/uCrop/blob/f788b534b48c144edf786c8cddbf0e029e637804/ucrop/src/main/jni/CImg.h#L33040-L33076","documentation":"CImg::solve() uses LAPACK sgels() for the least-squares/underdetermined path; nonzero INFO means sgels failed, either an invalid argument (bad dimensions/lwork) or the least-squares driver could not complete. CImg warns and falls back to (A.get_invert(use_LU)*X).","triggerScenarios":"Calling solve() on non-square A (over/under-determined systems) when sgels receives inconsistent M/N/NRHS/LDA/LDB/LWORK values or the problem is numerically degenerate.","commonSituations":"Fitting models with rank-deficient design matrices; dimension typos when building A and B; single-precision (sgels) limitations with badly scaled data.","solutions":["Verify A and this (B) have consistent, expected dimensions before solve()","Scale/normalize the data and use double precision to improve conditioning","Check for rank deficiency in A and remove dependent columns/rows","If the fallback (A^-1 * B) also fails, use a dedicated SVD-based pseudo-inverse","Inspect that your LAPACK provides sgels with the expected signature"],"exampleFix":"// before\nCImg<float> x = B.solve(A); // non-square A\n// after\nif (std::fabs(A.determinant()) < 1e-12f) {\n  for (int i = 0; i < A.width(); ++i) A(i,i) += 1e-6f; // regularize before least-squares\n}\nCImg<float> x = B.solve(A);","handlingStrategy":"validation","validationCode":"bool fitForLeastSquares(const CImg<float>& A, const CImg<float>& B) {\n  return A.width() > 0 && A.height() > 0 && B.height() == A.height() &&\n         !A.isnan().sum() && !B.isnan().sum();\n}","typeGuard":null,"tryCatchPattern":null,"preventionTips":["Validate shapes and NaN/Inf absence before solve()","Rank-check design matrices; drop dependent columns","Scale data and use double precision for bad conditioning","Have an SVD-based pseudo-inverse fallback ready"],"tags":["cimg","lapack","least-squares"],"backgroundTag":"lapack-solver-failed","analyzedSha":"f788b534b48c144edf786c8cddbf0e029e637804","analyzedAt":"2026-09-08T08:36:04.887Z","contentChangedAt":"2026-09-08T08:36:04.887Z","schemaVersion":2},"datasetVersion":"2026-09-14T11:17:12.474Z"}