xval[i] = -1 + 15 * i * delta;
yval[i] = -20 + 30 * i * delta;
}
// Function values
BivariateFunction f = new BivariateFunction() {
public double value(double x, double y) {
return 2 * x * x - 3 * y * y + 4 * x * y - 5;
}
};
double[][] zval = new double[xval.length][yval.length];
for (int i = 0; i < xval.length; i++) {
for (int j = 0; j < yval.length; j++) {
zval[i][j] = f.value(xval[i], yval[j]);
}
}
// Partial derivatives with respect to x
double[][] dZdX = new double[xval.length][yval.length];
BivariateFunction dfdX = new BivariateFunction() {
public double value(double x, double y) {
return 4 * (x + y);
}
};
for (int i = 0; i < xval.length; i++) {
for (int j = 0; j < yval.length; j++) {
dZdX[i][j] = dfdX.value(xval[i], yval[j]);
}
}
// Partial derivatives with respect to y
double[][] dZdY = new double[xval.length][yval.length];
BivariateFunction dfdY = new BivariateFunction() {
public double value(double x, double y) {
return 4 * x - 6 * y;
}
};
for (int i = 0; i < xval.length; i++) {
for (int j = 0; j < yval.length; j++) {
dZdY[i][j] = dfdY.value(xval[i], yval[j]);
}
}
// Partial cross-derivatives
double[][] dZdXdY = new double[xval.length][yval.length];
for (int i = 0; i < xval.length; i++) {
for (int j = 0; j < yval.length; j++) {
dZdXdY[i][j] = 4;
}
}
BivariateFunction bcf = new BicubicSplineInterpolatingFunction(xval, yval, zval,
dZdX, dZdY, dZdXdY);
double x, y;
final RandomGenerator rng = new Well19937c(1234567L); // "tol" depends on the seed.
final UniformRealDistribution distX
= new UniformRealDistribution(rng, xval[0], xval[xval.length - 1]);
final UniformRealDistribution distY
= new UniformRealDistribution(rng, yval[0], yval[yval.length - 1]);
final double tol = 224;
for (int i = 0; i < sz; i++) {
x = distX.sample();
for (int j = 0; j < sz; j++) {
y = distY.sample();
// System.out.println(x + " " + y + " " + f.value(x, y) + " " + bcf.value(x, y));
Assert.assertEquals(f.value(x, y), bcf.value(x, y), tol);
}
// System.out.println();
}
}