basis: add the basis of even cosines

2 files changed, 31 insertions, 0 deletions

diff --git a/basis.c b/basis.c
index face638..bb3a8e9 100644
--- a/basis.c
+++ b/basis.c
@@ -101,6 +101,33 @@ static const BasisSet sb_even_basis = {
     .colloc_point = sb_even_colloc_point,
 };
 
+static double cos_even_eval(const BasisSetContext *s, double coord, int idx)
+{
+    return cos(2 * idx * coord);
+}
+
+static double cos_even_eval_diff1(const BasisSetContext *s, double coord, int idx)
+{
+    return -2 * idx * sin(2 * idx * coord);
+}
+
+static double cos_even_eval_diff2(const BasisSetContext *s, double coord, int idx)
+{
+    return -4 * SQR(idx) * cos(2 * idx * coord);
+}
+
+static double cos_even_colloc_point(const BasisSetContext *s, int order, int idx)
+{
+    return M_PI * idx / (2 * order);
+}
+
+static const BasisSet cos_even_basis = {
+    .eval         = cos_even_eval,
+    .eval_diff1   = cos_even_eval_diff1,
+    .eval_diff2   = cos_even_eval_diff2,
+    .colloc_point = cos_even_colloc_point,
+};
+
 double bdi_basis_eval(BasisSetContext *s, enum BSEvalType type, double coord, int order)
 {
     double (*eval)(const BasisSetContext *s, double coord, int order);
@@ -138,6 +165,9 @@ BasisSetContext *bdi_basis_init(enum BasisFamily family, double sf)
         s->bs = &sb_even_basis;
         s->sf = sf;
         break;
+    case BASIS_FAMILY_COS_EVEN:
+        s->bs = &cos_even_basis;
+        break;
     default:
         free(s);
         return NULL;
diff --git a/basis.h b/basis.h
index 6b6f3c4..68c9597 100644
--- a/basis.h
+++ b/basis.h
@@ -26,6 +26,7 @@ enum BSEvalType {
 
 enum BasisFamily {
     BASIS_FAMILY_SB_EVEN,
+    BASIS_FAMILY_COS_EVEN,
 };
 
 typedef struct BasisSetContext BasisSetContext;