1 files changed, 56 insertions, 0 deletions
diff --git a/astro/cosmo_calc/ddivid.cc b/astro/cosmo_calc/ddivid.cc
new file mode 100644
index 0000000..aa72471
--- /dev/null
+++ b/astro/cosmo_calc/ddivid.cc
@@ -0,0 +1,56 @@
+#include <cassert>
+
+double ddivid(double (*foo)(double),double x1,double x2,double err)
+{
+  assert(x2>x1);
+  assert(foo(x2)*foo(x1)<0);
+  while(x2-x1>err)
+    {
+      double x=(x2+x1)/2.;
+      double y=foo(x);
+      double y1=foo(x1);
+      double y2=foo(x2);
+      if(y1*y<0)
+	{
+	  x2=x;
+	}
+      else if(y2*y<0)
+	{
+	  x1=x;
+	}
+      else
+	{
+	  assert(0);
+	}
+
+    }
+  return (x1+x2)/2.;
+}
+
+
+double ddivid(double (*foo)(double),double z,double x1,double x2,double err)
+{
+  assert(x2>x1);
+  assert((foo(x2)-z)*(foo(x1)-z)<0);
+  while(x2-x1>err)
+    {
+      double x=(x2+x1)/2.;
+      double y=foo(x)-z;
+      double y1=foo(x1)-z;
+      double y2=foo(x2)-z;
+      if(y1*y<0)
+	{
+	  x2=x;
+	}
+      else if(y2*y<0)
+	{
+	  x1=x;
+	}
+      else
+	{
+	  assert(0);
+	}
+
+    }
+  return (x1+x2)/2.;
+}