Fix: lstsq compilation with complex<float> inputs (#251)

This fix resolves a compilation error `gelsd.tcc:146:25: error: invalid
conversion from 'const float*' to 'cxxlapack::FLOAT_COMPLEX*'` when
linalg::lstsq is called with complex<float> arguments.
Note that `complex<double>` and other types were unaffected.

- A test case that demonstrates the issue is added to
test/test_linalg.cpp
- The fix adds const to the relevant interface to correctly match the
expected input data type
- The test compiles and passes with this fix

---------

Co-authored-by: Johan Mabille <[email protected]>

Author: deniz-unal

include/xflens/cxxlapack/netlib/interface/dummy.in.cc

@@ -1026,21 +1026,21 @@ LAPACK_DECL(cgels)(const char           *TRANS,
 
 //-- cgelsd --------------------------------------------------------------------
 void
-LAPACK_DECL(cgelsd)(const INTEGER    *M,
-                    const INTEGER    *N,
-                    const INTEGER    *NRHS,
-                    FLOAT_COMPLEX    *A,
-                    const INTEGER    *LDA,
-                    FLOAT_COMPLEX    *B,
-                    const INTEGER    *LDB,
-                    FLOAT            *S,
-                    const FLOAT      *RCOND,
-                    INTEGER          *RANK,
-                    FLOAT_COMPLEX    *WORK,
-                    const INTEGER    *LWORK,
-                    FLOAT            *RWORK,
-                    INTEGER          *IWORK,
-                    INTEGER          *INFO)
+LAPACK_DECL(cgelsd)(const INTEGER        *M,
+                    const INTEGER        *N,
+                    const INTEGER        *NRHS,
+                    const FLOAT_COMPLEX  *A,
+                    const INTEGER        *LDA,
+                    FLOAT_COMPLEX        *B,
+                    const INTEGER        *LDB,
+                    FLOAT                *S,
+                    const FLOAT          *RCOND,
+                    INTEGER              *RANK,
+                    FLOAT_COMPLEX        *WORK,
+                    const INTEGER        *LWORK,
+                    FLOAT                *RWORK,
+                    INTEGER              *IWORK,
+                    INTEGER              *INFO)
 {
     DEBUG_LAPACK_STUB("cgelsd");
     LAPACK_IMPL(cgelsd)(M,

include/xflens/cxxlapack/netlib/interface/lapack.in.h

@@ -579,21 +579,21 @@ LAPACK_IMPL(cgels)(const char           *TRANS,
 
 //-- cgelsd --------------------------------------------------------------------
 void
-LAPACK_IMPL(cgelsd)(const INTEGER    *M,
-                    const INTEGER    *N,
-                    const INTEGER    *NRHS,
-                    FLOAT_COMPLEX    *A,
-                    const INTEGER    *LDA,
-                    FLOAT_COMPLEX    *B,
-                    const INTEGER    *LDB,
-                    FLOAT            *S,
-                    const FLOAT      *RCOND,
-                    INTEGER          *RANK,
-                    FLOAT_COMPLEX    *WORK,
-                    const INTEGER    *LWORK,
-                    FLOAT            *RWORK,
-                    INTEGER          *IWORK,
-                    INTEGER          *INFO);
+LAPACK_IMPL(cgelsd)(const INTEGER        *M,
+                    const INTEGER        *N,
+                    const INTEGER        *NRHS,
+                    const FLOAT_COMPLEX  *A,
+                    const INTEGER        *LDA,
+                    FLOAT_COMPLEX        *B,
+                    const INTEGER        *LDB,
+                    FLOAT                *S,
+                    const FLOAT          *RCOND,
+                    INTEGER              *RANK,
+                    FLOAT_COMPLEX        *WORK,
+                    const INTEGER        *LWORK,
+                    FLOAT                *RWORK,
+                    INTEGER              *IWORK,
+                    INTEGER              *INFO);
 
 //-- cgelss --------------------------------------------------------------------
 void

test/test_linalg.cpp

@@ -491,6 +491,25 @@ namespace xt
             CHECK(allclose(cel_1, std::get<1>(cres)));
             CHECK_EQ(cel_2, std::get<2>(cres));
             CHECK(allclose(cel_3, std::get<3>(cres)));
+
+            xarray<std::complex<float>> cfarg_0 = {{0.f, 1.f}, {1.f - 3if, 1.f}, {2.f, 1.f}, {3.f, 1.f}};
+            xarray<std::complex<float>> cfarg_1 = {{-1.f, 0.2f + 4if, 0.9f, 2.1f - 1if}, {2.f, 3if, 2.f, 1.f}};
+            cfarg_1 = transpose(cfarg_1);
+            auto cfres = xt::linalg::lstsq(cfarg_0, cfarg_1);
+
+            xarray<std::complex<float>, layout_type::column_major> cfel_0 = {
+                {-0.40425532f - 0.38723404if, -0.61702128f - 0.44680851if},
+                {1.44680851f + 1.02765957if, 2.51063830f + 0.95744681if}
+            };
+            xarray<float> cfel_1 = {16.11787234f, 2.68085106f};
+            int cfel_2 = 2;
+            xarray<float> cfel_3 = {5.01295356f, 1.36758789f};
+
+            CHECK(allclose(imag(cfel_0), imag(std::get<0>(cfres))));
+            CHECK(allclose(real(cfel_0), real(std::get<0>(cfres))));
+            CHECK(allclose(cfel_1, std::get<1>(cfres)));
+            CHECK_EQ(cfel_2, std::get<2>(cfres));
+            CHECK(allclose(cfel_3, std::get<3>(cfres)));
         }
 
         TEST_CASE("trace")