输入字符类型算式，进行四则运算，支持括号和括号嵌套，用递归算法，支持科学计数法-Enter the character type formula for four operations, support brackets and parentheses nested, recursive algorithm, support scientific notation

Fast Symmetric Positive Definite Matrix Inverse by Eric Blake Uses LAPACK, Cholesky to invert real, positive definite, symmetric matrix. Faster than inv.