add root finding

README.md

@@ -1,5 +1,7 @@
 ## C++ cubic spline interpolation
 
+![cubic C2 spline](https://kluge.in-chemnitz.de/opensource/spline/cubic_c2_spline_git.png)
+
 This is a lightweight implementation of **cubic splines**
 to interpolate points f(x<sub>i</sub>) = y<sub>i</sub> with
 the following features.
@@ -27,6 +29,7 @@ be used like this:
     tk::spline s(X,Y);			// X needs to be strictly increasing
     double value=s(1.3);		// interpolated value at 1.3
     double deriv=s.deriv(1,1.3);	// 1st order derivative at 1.3
+    std::vector<double> solutions = s.solve(0.0);	// solves s(x)=0.0
     ...
 ```
 
@@ -47,7 +50,6 @@ This is identical to (must be called in that order):
     s.make_monotonic();
 ```
 
-![cubic C2 spline](https://kluge.in-chemnitz.de/opensource/spline/cubic_c2_spline_git.png)
 
 ### Spline types
 Splines are piecewise polynomial functions to interpolate points

examples/Makefile

@@ -14,7 +14,7 @@ CFLAGS += -DHAVE_SSTREAM		# whether compiler has <sstream>
 LFLAGS=
 
 
-PROGS=simple_demo plot plot_avg_preserv plot_parametric plot_bspline
+PROGS=simple_demo plot plot_avg_preserv plot_parametric plot_bspline cubic_root
 PROGS_ALGLIB=plot_alglib bench
 PROGS_TESTS=tests/unit_tests tests/compile_units tests/simple_demo_c98
 
@@ -34,6 +34,8 @@ plot_parametric:	plot_parametric.o
 		${CC} $< -o $@
 plot_bspline:	plot_bspline.o
 		${CC} $< -o $@
+cubic_root:	cubic_root.o gsl_solve_cubic.o
+		${CC} $^ -o $@
 
 tests/compile_units:	tests/compile_units.o tests/myfunc1.o tests/myfunc2.o
 		${CC} $? -o $@