Add function integ to control language

Trapezoidal rule for integrating a vector.

examples/various/integrate1.cir

@@ -0,0 +1,28 @@
+Test of integ
+
+i1 0 1 1
+R1 1 2 1
+C1 2 3 1 ic=0
+Vm1 3 0 0
+
+v2 11 0 dc 0 sin (0 1 2)
+
+v3 31 0 dc 0 pulse (0 1 0.1 0.1 0.1 0.1 0.6)
+
+.tran 0.01 1
+
+.control
+run
+display
+let int1 = integ(Vm1#branch)
+
+plot int1 v(2)
+
+let int2 = integ(v(11))
+plot v(11) int2
+
+let int3 = integ(v(31))
+plot v(31) int3
+
+.endc
+.end

src/frontend/evaluate.c

@@ -838,7 +838,7 @@ apply_func_funcall(struct func *func, struct dvec *v, int *newlength, short int
     /* Modified for passing necessary parameters to the derive function - A.Roldan */
 
     if (eq(func->fu_name, "interpolate") || eq(func->fu_name, "deriv") || eq(func->fu_name, "group_delay")
-        || eq(func->fu_name, "fft") || eq(func->fu_name, "ifft"))       /* Ack */
+        || eq(func->fu_name, "fft") || eq(func->fu_name, "ifft") || eq(func->fu_name, "integ"))
     {
         void * (*f) (void *data, short int type, int length,
                      int *newlength, short int *newtype,

src/frontend/parse.c

@@ -363,6 +363,7 @@ struct func ft_funcs[] = {
     { "vecd",        cx_d },
     { "interpolate", (cx_function_t*) cx_interpolate },
     { "deriv",       (cx_function_t*) cx_deriv },
+    { "integ",       (cx_function_t*) cx_integ },
     { "fft",         (cx_function_t*) cx_fft },
     { "ifft",        (cx_function_t*) cx_ifft },
     { "v",           NULL },

src/include/ngspice/fteext.h

@@ -123,6 +123,7 @@ extern void *cx_not(void *, short int , int , int *, short int *);
 
 extern void *cx_interpolate(void *, short int , int , int *, short int *, struct plot *, struct plot *, int );
 extern void *cx_deriv(void *, short int , int , int *, short int *, struct plot *, struct plot *, int );
+extern void *cx_integ(void *, short int , int , int *, short int *, struct plot *, struct plot *, int );
 extern void *cx_group_delay(void *, short int , int , int *, short int *, struct plot *, struct plot *, int );
 extern void *cx_fft(void *, short int , int , int *, short int *, struct plot *, struct plot *, int );
 extern void *cx_ifft(void *, short int , int , int *, short int *, struct plot *, struct plot *, int );

src/maths/cmaths/cmath4.c

@@ -435,6 +435,56 @@ cx_deriv(void *data, short int type, int length, int *newlength, short int *newt
 
 }
 
+/* integrate a vector using trapezoidal rule */
+void*
+cx_integ(void* data, short int type, int length, int* newlength, short int* newtype, struct plot* pl, struct plot* newpl, int grouping)
+{
+    if (grouping == 0)
+        grouping = length;
+    /* First do some sanity checks. */
+    if (!pl || !pl->pl_scale || !newpl || !newpl->pl_scale) {
+        fprintf(cp_err, "Internal error: cx_integ: bad scale\n");
+        return (NULL);
+    }
+
+    *newlength = length;
+    *newtype = type;
+
+    if (type == VF_COMPLEX) {
+        fprintf(cp_err, "Error: Function integ is not supported for complex data\n");
+        return (NULL);
+    }
+    else
+    {
+        /* all-real case */
+        double* outdata, * indata;
+        double* scale;
+        int i;
+        double delta;
+
+        indata = (double*)data;
+        outdata = alloc_d(length);
+        scale = alloc_d(length);
+
+         /* Modified to deal with complex frequency vector */
+        if (iscomplex(pl->pl_scale))
+            for (i = 0; i < length; i++)
+                scale[i] = realpart(pl->pl_scale->v_compdata[i]);
+        else
+            for (i = 0; i < length; i++)
+                scale[i] = pl->pl_scale->v_realdata[i];
+
+        /* use trapezoidal rule */
+        outdata[0] = 0;
+        for (i = 1; i < length; i++) {
+            delta = scale[i] - scale[i - 1];
+            outdata[i] = outdata[i - 1] + (indata[i] + indata[i - 1]) * delta / 2.;
+        }
+
+        tfree(scale);
+        return (char*)outdata;
+    }
+}
 
 void *
 cx_group_delay(void *data, short int type, int length, int *newlength, short int *newtype, struct plot *pl, struct plot *newpl, int grouping)

src/maths/cmaths/cmath4.h

@@ -13,6 +13,8 @@ void * cx_interpolate(void *data, short int type, int length, int *newlength,
 		      short int *newtype, struct plot *pl, struct plot *newpl, int grouping);
 void * cx_deriv(void *data, short int type, int length, int *newlength, short int *newtype, 
 		struct plot *pl, struct plot *newpl, int grouping);
+void * cx_integ(void *data, short int type, int length, int *newlength, short int *newtype,
+		struct plot *pl, struct plot *newpl, int grouping);
 void * cx_group_delay(void *data, short int type, int length, int *newlength, short int *newtype, 
 		struct plot *pl, struct plot *newpl, int grouping);
 void * cx_fft(void *data, short int type, int length, int *newlength, short int *newtype,