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第 2 章符号计算2.1符号对象和符号表达式2.1.1符号对象的创建和衍生1生成符号对象的基本规则2符号数字和符号常数【例2.1-1】a=pi+sqrt(5)sa=sym('pi+sqrt(5)')Ca=class(a)Csa=class(sa)vpa(sa-a)a =5.3777sa =pi + 5^(1/2)Ca =doubleCsa =symans =0.0000000000000000138223758410852000485935425641883基本符号变量4自由符号变量【例2.1-2】。
（1）syms u v w z a5f=sym('3');Eq=sin(f)*u*z^2+v*z+f*w-a5;（2）symvar(Eq)ans =[ a5, u, v, w, z]symvar(Eq,100)ans =[ w, z, v, u, a5]symvar(Eq,1)ans =w（3）result_1=solve(Eq)result_1 =a5/3 - (v*z)/3 - (u*sin(3)*z^2)/3（4）result_2=solve(Eq,z)result_2 =-(v - (v^2 + 4*a5*u*sin(3) - 12*u*w*sin(3))^(1/2))/(2*u*sin(3)) -(v + (v^2 + 4*a5*u*sin(3) - 12*u*w*sin(3))^(1/2))/(2*u*sin(3))【例2.1-3】（1）syms a b x X Yk=sym('3');z=sym('c*sqrt(d)+y*sin(t)');EXPR=a*z*X+(b*x^2+k)*Y;（2）symvar(EXPR)ans =[ X, Y, a, b, c, d, t, x, y]（3）symvar(EXPR,10)ans =[ x, y, t, d, c, b, a, X, Y]（4）symvar(EXPR,1)ans =x（5）symvar(EXPR,3)ans =[ x, y, t]（6）E3=sym('a*sqrt(theta)')??? Error using ==> sym.sym>sym.sym/scalarsym at 382Error: argument must be of 'Type::Arithmetical' [sqrt]Error in ==> sym.sym>sym.sym/char2sym at 337Scell = scalarsym(x);Error in ==> sym.sym>sym.sym/symchar at 182Scell = char2sym(x);Error in ==> sym.sym>sym.sym at 120S = cell2sym(S,symchar(x,a,nargin));E4=sym('a*sqrt(theta123)')E4 =a*theta123^(1/2)E5=sym('a*sqrt(theta*t)')E5 =a*(t*theta)^(1/2)【例2.1-4】syms a b t u v x yA=[a+b*x,sin(t)+u;x*exp(-t),log(y)+v] symvar(A,1)A =[ a + b*x, u + sin(t)][ x/exp(t), v + log(y)]ans =x2.1.2符号计算中的算符2.1.3符号计算中的函数指令2.1.4符号对象的识别【例2.1-5】。
