matlab错误提示R_tilde = builtin()

已知几个参数的关系式，求其中一个参数pi1的表达式

clear all;
clc;
syms a b  ct cs u2 u1 w   
p1 =(a-b*ct)/(2*b*(1-w*u2+w*(1-u1-u2)));
q = (a+b*p1*w*u2-b*p1-b*ct-b*p1*w(1-u1-u2));
pi1 = q*(p1-cs-p1*w*u1);
simple_pi1 = simplify(pi1);
pretty(simple_pi1)

提示
出错 sym/subsref (line 890)
R_tilde = builtin('subsref',L_tilde,Idx);

出错 anyway (line 5)
q = (a+bp1wu2-bp1-bct-bp1*w(1-u1-u2));

你好，缺少了个乘号，补上了

clear all;
clc;
syms a b  ct cs u2 u1 w   
p1 =(a-b*ct)/(2*b*(1-w*u2+w*(1-u1-u2)));
q = (a+b*p1*w*u2-b*p1-b*ct-b*p1*w*(1-u1-u2)); % w后面缺少乘号，补上了
pi1 = q*(p1-cs-p1*w*u1);
simple_pi1 = simplify(pi1);
pretty(simple_pi1)

结果

(a - b ct) (a - 2 b cs - b ct - 2 b cs w - a u1 w + 2 b cs u1 w + 4 b cs u2 w + b ct u1 w)
------------------------------------------------------------------------------------------
                                b (w - u1 w - 2 u2 w + 1) 4