eval not working for a range of numbers
1 vue (au cours des 30 derniers jours)
Afficher commentaires plus anciens
I have typed a code for the position of a mechanism with 6 links using vector loop equations with Euler. My code works from theta2 = 0*pi/180 to 97*pi/180. It also works around 330 degrees and higher. Why does it not work at 98 degrees or higher?
clc,clear
format shortg
% known values
Crank = 0.10 ; % length in meters
AB = 0.20 ; % legnth in meters
BC = 0.113 ; % length in meters
Link4 = 0.35 ; % length in meters
theta2 = 0*pi/180 ; % radians
%% Position
% known vectors
Crank_ = Crank*[cos(theta2) sin(theta2) 0] ;
Ground1_ = [0.1646 0.0250 0] ; % O2 to O6, meters
Ground2_ = [0.197 -0.2262 0] ; % O2 to O4, meters
Ground3_ = [0.0324 -0.2512 0] ; % O6 to O4, meters
% create symbolic variables
syms thetaAB theta4
% set assumptions
assume(theta4 >= 0 & theta4 <= pi)
assume(thetaAB >= 0 & thetaAB <= pi/2)
thetaBC = thetaAB - 64*pi/180 ;
% convert to polar coordinates
[theta_g1,Ground1] = cart2pol(Ground1_(1),Ground1_(2)) ;
[theta_g2,Ground2] = cart2pol(Ground2_(1),Ground2_(2)) ;
[theta_g3,Ground3] = cart2pol(Ground3_(1),Ground3_(2)) ;
% set up equations
Pos1 = Ground2*cos(theta_g2) + Link4*cos(theta4) - Crank*cos(theta2) - AB*cos(thetaAB) ;
Pos2 = Ground2*1i*sin(theta_g2) + Link4*1i*sin(theta4) - Crank*1i*sin(theta2) - AB*1i*sin(thetaAB) ;
% solve
sol = solve(Pos1, Pos2, thetaAB, theta4) ;
thetaAB = eval(sol.thetaAB) ;
theta4 = eval(sol.theta4) ;
% second syms to find theta6 and O6_C
syms theta6 O6_C
assume(O6_C >= 0 & O6_C <= 0.24)
assume(theta6 >= 0 & theta6 <= pi)
% set up equations
Pos3 = Ground1*cos(theta_g1) + O6_C*cos(theta6) - Crank*cos(theta2) - AB*cos(thetaAB) - BC*cos(thetaBC) ;
Pos4 = Ground1*1i*sin(theta_g1) + O6_C*1i*sin(theta6) - Crank*1i*sin(theta2) - AB*1i*sin(thetaAB) - BC*1i*sin(thetaBC) ;
% solve
sol = solve(Pos3, Pos4, theta6, O6_C) ;
theta6 = eval(sol.theta6) ;
O6_C = eval(sol.O6_C) ;
0 commentaires
Réponses (2)
Steven Lord
le 6 Avr 2021
There's no need for eval.
% known values
Crank = 0.10 ; % length in meters
AB = 0.20 ; % legnth in meters
BC = 0.113 ; % length in meters
Link4 = 0.35 ; % length in meters
theta2 = 0*pi/180 ; % radians
%% Position
% known vectors
Crank_ = Crank*[cos(theta2) sin(theta2) 0] ;
Ground1_ = [0.1646 0.0250 0] ; % O2 to O6, meters
Ground2_ = [0.197 -0.2262 0] ; % O2 to O4, meters
Ground3_ = [0.0324 -0.2512 0] ; % O6 to O4, meters
% create symbolic variables
syms thetaAB theta4
% set assumptions
assume(theta4 >= 0 & theta4 <= pi)
assume(thetaAB >= 0 & thetaAB <= pi/2)
thetaBC = thetaAB - 64*pi/180 ;
% convert to polar coordinates
[theta_g1,Ground1] = cart2pol(Ground1_(1),Ground1_(2)) ;
[theta_g2,Ground2] = cart2pol(Ground2_(1),Ground2_(2)) ;
[theta_g3,Ground3] = cart2pol(Ground3_(1),Ground3_(2)) ;
% set up equations
Pos1 = Ground2*cos(theta_g2) + Link4*cos(theta4) - Crank*cos(theta2) - AB*cos(thetaAB) ;
Pos2 = Ground2*1i*sin(theta_g2) + Link4*1i*sin(theta4) - Crank*1i*sin(theta2) - AB*1i*sin(thetaAB) ;
% solve
sol = solve(Pos1, Pos2, thetaAB, theta4) ;
thetaAB = sol.thetaAB
theta4 = sol.theta4
If you need the numeric values of thetaAB and theta4:
thetaAB_double = double(thetaAB)
thetaAB_vpa = vpa(thetaAB)
theta4_double = double(theta4)
theta4_vpa = vpa(theta4)
0 commentaires
Image Analyst
le 5 Avr 2021
Why are you even using eval at all instead of simply doing this:
thetaAB = sol.thetaAB;
theta4 = sol.theta4;
???
2 commentaires
Image Analyst
le 5 Avr 2021
I don't know. I don't use syms. He may be right. But do you need to use syms? Can't you define theta over some range with linspace() and do it numerically? What does this show:
whos sol
Voir également
Catégories
En savoir plus sur Number Theory dans Help Center et File Exchange
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!