解微分方程组

有三个方程:

y1''(x) + A1 * y3(x) + A2 * y2(x) + A3 = 0
y1''(x) + B1 * y2''(x) + B2 * y1(x) * y2(x) + B3 = 0
y1''(x) + C1 * y3''(x) + C2 * y1(x) * y2(x) + C3 =0

A, B, C是常数 a < x < b
初值y1(a), y1'(a), y2(a), y2'(a), y3(a), y3'(a) 已知

请问如何数值求解？