Error using evalin Undefined function or variable 'x'. Error in sym/eval (line 11) s = evalin('ca​ller',vect​orize(map2​mat(char(x​))));

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Maria Giulia
Maria Giulia 2020-11-22
评论： Stephen23 2020-11-23
i was trying to solve a simple system of equations, when the program gives me this error:
Error using evalin
Undefined function or variable 'x'.
Error in sym/eval (line 11)
s = evalin('caller',vectorize(map2mat(char(x))));
Error in es_6_analisi_cinematica (line 27)
xBposizioni=eval(solB.xBsol);
in fact when I go to evaluate the solutions of the system inside solB, it solves the system in x and y, rather than xBsol and yBsol. sorry that the script may seem strange but I'm Italian
i get the same problem using vpa instead of eval, the system of equations is solved with other variables, x and y
This is the script:
clear
AC=0.15;
BC=0.2;
AD=0.35;
xA=0;
yA=0;
rA=[xA yA 0];
xC=AC;
yC=0;
rC=[xC yC 0];
ii=0;
for phi=10^(-17):pi/36:2*pi
xD=AD*cos(phi);
yD=AD*sin(phi);
rD=[xD yD 0];
xBsol=sym('xBsol');
yBsol=sym('yBsol');
eqB1='xBsol*sin(phi)-yBsol*cos(phi)=0';
eqB2='(xC-xBsol)^2+yBsol^2-BC^2=0';
solB=solve(eqB1,eqB2,'xBsol','yBsol');
xBposizioni=eval(solB.xBsol);
yBposizioni=eval(solB.yBsol);
xB1=xBposizioni(1)
yB1=yBposizioni(1)
xB2=xBposizioni(2)
yB2=yBposizioni(2)
if (phi>=0 && phi<=pi)
if yB1>=0 xB=xB1;yB=yB1;
else
xB=xB2;yB=yB2;
end
end
if (phi>pi && phi< 2*pi)
if yB1<0
xB=xB1; yB=yB1;
else
xB=xB2; yB=yB2;
end
end
rB=[xB yB 0];
figure(1)
plot([xA,xB],[yA,yB],'k-',[xB, xC],[yB,yC],'r-',[xA,xC],[yA,yC],'b-',[xB,xD],[yB,yD],'g-')
text(xA,yA,'A')
text(xB,yB,'B')
text(xC,yC,'C')
text(xD,yD,'D')
hold on
xlim([-0.5 0.5])
ylim([-0.5 0.5])
end

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采纳的回答

Stephan
Stephan 2020-11-23
编辑：Stephan 2020-11-23
clear
AC=0.15;
BC=0.2;
AD=0.35;
xA=0;
yA=0;
rA=[xA yA 0];
xC=AC;
yC=0;
rC=[xC yC 0];
syms xBsol yBsol
ii=0;
for phi=10^(-17):pi/36:2*pi
xD=AD*cos(phi);
yD=AD*sin(phi);
rD=[xD yD 0];
eqB1=xBsol*sin(phi)-yBsol*cos(phi)==0;
eqB2=(xC-xBsol)^2+yBsol^2-BC^2==0;
solB=solve(eqB1,eqB2,xBsol,yBsol);
xBposizioni=eval(solB.xBsol);
yBposizioni=eval(solB.yBsol);
xB1=xBposizioni(1);
yB1=yBposizioni(1);
xB2=xBposizioni(2);
yB2=yBposizioni(2);
if (phi>=0 && phi<=pi)
if yB1>=0
xB=xB1;
yB=yB1;
else
xB=xB2;yB=yB2;
end
end
if (phi>pi && phi< 2*pi)
if yB1<0
xB=xB1; yB=yB1;
else
xB=xB2; yB=yB2;
end
end
rB=[xB yB 0];
figure(1)
plot([xA,xB],[yA,yB],'k-',[xB, xC],[yB,yC],'r-',[xA,xC],[yA,yC],'b-',[xB,xD],[yB,yD],'g-')
text(xA,yA,'A')
text(xB,yB,'B')
text(xC,yC,'C')
text(xD,yD,'D')
hold on
xlim([-0.5 0.5])
ylim([-0.5 0.5])
end

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