Add docstring to SparseCG and MatrixFreeCG.

python/taichi/linalg/matrixfree_cg.py

@@ -17,6 +17,20 @@ def matvec(self, x, Ax):
 
 
 def MatrixFreeCG(A, b, x, tol=1e-6, maxiter=5000, quiet=True):
+    """Matrix-free conjugate-gradient solver.
+    
+    Use conjugate-gradient method to solve the linear system Ax = b, where A is implicitly
+    represented as a LinearOperator.
+
+    Args:
+        A (LinearOperator): The coefficient matrix A of the linear system.
+        b (Field): The right-hand side of the linear system.
+        x (Field): The initial guess for the solution.
+        maxiter (int): Maximum number of iterations.
+        atol: Tolerance(absolute) for convergence.
+        quiet (bool): Switch to turn on/off iteration log.
+    """
+
     if b.dtype != x.dtype:
         raise TaichiTypeError(f"Dtype mismatch b.dtype({b.dtype}) != x.dtype({x.dtype}).")
     if str(b.dtype) == "f32":

python/taichi/linalg/sparse_cg.py

@@ -7,6 +7,18 @@
 
 
 class SparseCG:
+    """Conjugate-gradient solver built for SparseMatrix.
+    
+    Use conjugate-gradient method to solve the linear system Ax = b, where A is SparseMatrix.
+
+    Args:
+        A (SparseMatrix): The coefficient matrix A of the linear system.
+        b (numpy ndarray, taichi Ndarray): The right-hand side of the linear system.
+        x0 (numpy ndarray, taichi Ndarray): The initial guess for the solution.
+        max_iter (int): Maximum number of iterations.
+        atol: Tolerance(absolute) for convergence.
+    """
+
     def __init__(self, A, b, x0=None, max_iter=50, atol=1e-6):
         self.dtype = A.dtype
         self.ti_arch = get_runtime().prog.config().arch