fix(quadrature): optimize Gauss-Legendre and tanh-sinh integration calculations，support integral over [a, b]

surface_integral/include/quadrature.hpp

@@ -3,25 +3,27 @@
 #include "GL_integrator.hpp"
 #include "TS_integrator.hpp"
 
-// 高斯-勒让德一维积分：积分区间 [a, b]
+// Gauss-Legendre quadrature for 1D integral over interval [a, b]
 template<typename Func>
 double gauss_integrate_1D(double a, double b, Func&& func, int q) {
     double sum = 0.0;
+    double length = b - a;
     for (int i = 0; i < q; ++i) {
-        double x = GLIntegrator<double>::x(q, i, a, b);
+        double x = a + length * GLIntegrator<double>::x(q, i);
-        double w = GLIntegrator<double>::w(q, i, a, b);
+        double w = length * GLIntegrator<double>::w(q, i);
         sum += w * func(x);
     }
     return sum;
 }
 
-// tanh-sinh 一维积分：积分区间 [a, b]
+// Tanh-sinh quadrature for 1D integral over [a, b]
 template<typename Func>
 double tanh_sinh_integrate_1D(double a, double b, Func&& func, int q) {
     double result = 0.0;
+    double length = b - a;
     for (int i = 0; i < q; ++i) {
-        double x = TSIntegrator<double>::x(q, i, a, b);
+        double x = a + length * TSIntegrator<double>::x(q, i, a, b);
-        double w = TSIntegrator<double>::w(q, i, a, b);
+        double w = length * TSIntegrator<double>::w(q, i, a, b);
         result += w * func(x);
     }
     return result;