void spolint (const float *xa, const float *ya, int_t n,
float x, float *y, float *dy)
{
register int_t ns = 1;
#if defined(__uxp__) || defined(_SX)
float dif = (float) fabs (x - xa[1]),
#else
float dif = fabsf(x - xa[1]),
#endif
*c = svector(1, n),
*d = svector(1, n);
register int_t i, m;
float den, dift, ho, hp, w;
for (i = 1; i <= n; i++) {
#if defined(__uxp__) || defined(_SX)
if ((dift = (float) fabs (x - xa[1])) < dif) {
#else
if ((dift = fabsf (x - xa[i])) < dif) {
#endif
ns = i;
dif = dift;
}
c[i] = ya[i];
d[i] = ya[i];
}
*y = ya[ns--];
for (m = 1; m < n; m++) {
for (i = 1; i <= n - m; i++) {
ho = xa[i] - x;
hp = xa[i+m] -x;
w = c[i+1] - d[i];
if( (den = ho-hp) == 0.0F)
message("spolint()", "two x values the same (within roundoff)", ERROR);
den = w / den;
d[i] = hp * den;
c[i] = ho * den;
}
*y += (*dy=((ns<<1) < (n-m) ? c[ns+1] : d[ns--]));
}
freeSvector (c, 1);
freeSvector (d, 1);
}
void sspline (integer n, float yp1, float ypn, const float* x, const float* y,
float* y2)
{
register integer i, k;
float h = x[1] - x[0],
*u = svector(0, n-2);
float p, qn, sig, un, hh;
if (yp1 > 0.99e30)
y2[0] = u[0] = 0.0F;
else {
y2[0] = -0.5F;
u [0] = (3.0F / h) * ((y[1]-y[0]) / h - yp1);
}
for (i = 1; i < n-1; i++) {
hh = 1. / (x[i+1] - x[i-1]);
sig = h * hh;
p = sig * y2[i-1] + 2.;
y2[i] = (sig - 1.) / p;
u [i] = (y[i] - y[i-1]) / h;
u [i] = (y[i+1] - y[i]) / (h = x[i+1]-x[i]) - u[i];
u [i] = (6.0F * u[i] * hh - sig * u[i-1])/p;
}
if (ypn > 0.99e30)
qn = un = 0.0F;
else {
qn = 0.5F;
un = (3.0F / h)*(ypn - (y[n-1]-y[n-2])/h);
}
y2[n-1] = (un - qn * u[n-2]) / (qn * y2[n-2] + 1.);
for (k = n-2; k; k--) y2[k] = y2[k] * y2[k+1] + u[k];
freeSvector(u, 0);
}
