fixed external blas with gfortran

updated readme

Author: jacobwilliams

README.md

@@ -84,6 +84,10 @@ The library also contains routines for computing definite integrals of bsplines.
 
 Note that extrapolation is not currently supported for these.
 
+## Least squares fitting
+
+The BSpline-Fortran library also exports the `defc` subroutine, which can be used to fit B-spline polynomials to 1D data using a weighted least squares method.
+
 ## Examples
 
 See the [examples](https://github.com/jacobwilliams/bspline-fortran/tree/master/src/tests) for more details. Note that, to compile and run some of the test programs, the [pyplot_module.f90](https://github.com/jacobwilliams/pyplot-fortran) file (which is used to generate plots) must be copied into the `src/tests` directory.
@@ -160,6 +164,16 @@ For a debug build:
  cmake -DCMAKE_BUILD_TYPE=DEBUG ..
 ```
 
+## Dependencies
+
+The library requires some [BLAS](https://netlib.org/blas/) routines, which are included. However, the user may also choose to link to an external BLAS library. This can be done by using the `HAS_BLAS` compiler directive. For example:
+
+```
+fpm build --compiler gfortran --flag "-DHAS_BLAS -lblas"
+```
+
+However, note that an external BLAS can only be used if the library is compiled with double precision (`real64`) reals.
+
 ## Documentation
 
 The latest API documentation can be found [here](https://jacobwilliams.github.io/bspline-fortran/). This was generated from the source code using [FORD](https://github.com/Fortran-FOSS-Programmers/ford) (i.e. by running `ford bspline-fortran.md`).

src/bspline_blas_module.F90

@@ -16,19 +16,19 @@
 !  * [BLAS Sourcecode](https://github.com/Reference-LAPACK/lapack/tree/master/BLAS/SRC)
 
 module bspline_blas_module
+
 #ifndef HAS_BLAS
 
    use bspline_kinds_module, only: wp, ip
 
    implicit none
-
    private
 
    public :: daxpy,dcopy,dscal,dswap,ddot
 
 contains
 
-   subroutine daxpy(n, da, dx, incx, dy, incy)
+    subroutine daxpy(n, da, dx, incx, dy, incy)
          !! DAXPY constant times a vector plus a vector.
          !! uses unrolled loops for increments equal to one.
 

src/bspline_defc_module.f90 renamed to src/bspline_defc_module.F90

@@ -8,12 +8,19 @@
 module bspline_defc_module
 
    use bspline_kinds_module, only: wp !, ip
+#ifndef HAS_BLAS
    use bspline_blas_module
+#endif
 
    implicit none
 
    private
 
+#ifdef HAS_BLAS
+   double precision,external :: ddot
+   external :: daxpy,dcopy,dscal,dswap
+#endif
+
    public :: defc
 
    contains