符号变量的创建–syms clear,clcsyms a x;%定义符号变量y = a*x+x^2;y = str2sym('a*x+x^2');%R2017版本之后，字符串转变为符号方程 y = a*x + x^2 y = a*x + x^2 符号矩阵 syms alpha;M = [cos(alpha) -sin(alpha); sin(alpha) cos(alpha)] M = [ cos(alpha), -sin(alpha)][ sin(alpha), cos(alpha)] 符号表达式的整理 clear,clc; syms a; y = (cot(a/2)-tan(a/2))*(1+tan(a)*tan(a/2)); simplify(y); y = (cot(a/2) - tan(a/2))*(tan(a/2)*tan(a) + 1) ans = 2/sin(a) 因式分解–factor clear,clc; factor(12)%对常数进行因式分解 ans = 2 2 3 syms m n x; y = -24*m^2*x-16*n^2*x ans = [ -8, x, 2*n^2 + 3*m^2] y1 = m^3-n^3 factor(y1) y1 =- n^3 + m^3 ans = [ - n + m, n^2 + m*n + m^2] 多项式展开–expand clear,clc;syms a x;y = a*(x^2-a)^2+(x-2)expand(y) y = x + a*(a - x^2)^2 - 2 ans = - 2 + a^3 + x - 2*a^2*x^2 + a*x^4 多项式合并–collect clear,clc;syms x y;z = (x+y)^2*y+5*y*x-2*x^3expand(z);collect(z,x)%合并成x为自变量的多项式，y为系数 % y*x^2 - 2*x^3 + (5*y + 2*y^2)*x + y^3collect(z,y)%合并成y为自变量的多项式，x为系数 % y^3 + 2*x*y^2 + (5*x + x^2)*y - 2*x^3 % y*x^2 - 2*x^3 + (5*y + 2*y^2)*x + y^3% y^3 + 2*x*y^2 + (5*x + x^2)*y - 2*x^3 计算分子与分母–numden
syms 与 sym 命令不同，后者使用需要括号
% [z1,z2] = numden(2.5)----这样使用会报错，必须使用sym先定义clear,clc;[z1,z2] = numden(sym(2.5)); z1 = 5 z2 =2 syms x y;z = 1/(x*y)+x/(x^2-2*y);[z1,z2] = numden(z); z = 1/(x*y) - x/(2*y - x^2) z1 = 2*y - x^2 - x^2*y z2 =x*y*(2*y - x^2)