delete a line in a for loop with MATLAB - matlab

Question

i'm struggling with this matter probably
i'm just starting with Matlab.this is my code,i
wanna rotate a two links arm,using rotation matrix:
clear all
close all
clc
myaxes = axes('Xlim',[-1 1 ],'Ylim',[-1 1],'Zlim',[-1 1]);
view(3);
grid on;
axis equal;
hold on
xlabel('X')
ylabel('y')
zlabel('Z')
P_0 = [0; 0; 0] ;
P_1 = [-0.5;0; 0] ;
P_2 = [-1; 0; 0] ;
alfa_1 = 0:1:30 ;
alfa_2 =(0:0.5:15) ;
for i = 1:length(alfa_1)
M3(:,:,i) = [cosd(alfa_1(i)) -sind(alfa_1(i)) 0
sind(alfa_1(i)) cosd(alfa_1(i)) 0
0 0 1] ;
P_1(:,i,i) = M3(:,:,i)*[-0.5;0; 0] ;
P_2(:,i,i) = M3(:,:,i)*[-1;0; 0];
figure(1)
line([0 P_1(1,i,i)],[0 P_1(2,i,i)],[0 P_1(3,i,i)]);
scatter(P_1(1,i,i),P_1(2,i,i));
hold on
M3_1(:,:,i) = [cosd(alfa_2(i)) -sind(alfa_2(i)) 0
sind(alfa_2(i)) cosd(alfa_2(i)) 0
0 0 1] ;
P_2_2(:,i,i) = M3_1(:,:,i)*P_2(:,i,i);
line([P_1(1,i,i) P_2_2(1,i,i)],[P_1(2,i,i) P_2_2(2,i,i)],[P_1(3,i,i) P_2_2(3,i,i)],'color','r');
scatter(P_2_2(1,i,i), P_2_2(2,i,i))
hold on
end
should i use delete function to obtain an animation without plotting
all the lines but only the current line?!?.
thanks in advance for your help and support.

Answer 1

You can use the drawnow function in MATLAB for this purpose. This function can be used inside a for loop to force a plot to be rendered every iteration, instead of being stored in a buffer until after the loop.
Update figure window and execute pending callbacks
An example: for a simpler code consider a object moves on circle
t = 0:0.05:2*pi;
x = cos(t);
y = sin(t);
for k=1:length(t)
plot(x(k),y(k),'ko')
axis([-1.2 1.2 -1.2 1.2])
axis square
drawnow
end
Please note the axis function in this method. If the axis lines are deleted from the code then, in every iteration, the axis limits will change and the animation is not smooth.
What about your code:
clear all
close all
clc
view(3);
xlabel('X');
ylabel('y');
zlabel('Z');
P_0 = [0; 0; 0] ;
P_1 = [-0.5;0; 0] ;
P_2 = [-1; 0; 0] ;
alfa_1 = 0:1:30 ;
alfa_2 = (0:0.5:15) ;
for i = 1:length(alfa_1)
% Calculate new values for plotting
M3(:,:,i) = [cosd(alfa_1(i)), -sind(alfa_1(i)), 0
sind(alfa_1(i)), cosd(alfa_1(i)), 0
0 , 0 , 1] ;
P_1(:,i,i) = M3(:,:,i)*[-0.5; 0; 0] ;
P_2(:,i,i) = M3(:,:,i)*[-1; 0; 0] ;
% Clear figure 1 and hold for all plots
figure(1)
clf
% Hold only needs to be applied around plots on same axes
hold on
line([0 P_1(1,i,i)],[0 P_1(2,i,i)],[0 P_1(3,i,i)]);
scatter(P_1(1,i,i),P_1(2,i,i));
% Recalculate plotting values
M3_1(:,:,i) = [cosd(alfa_2(i)), -sind(alfa_2(i)), 0
sind(alfa_2(i)), cosd(alfa_2(i)), 0
0 , 0 , 1] ;
P_2_2(:,i,i) = M3_1(:,:,i)*P_2(:,i,i);
line([P_1(1,i,i) P_2_2(1,i,i)], [P_1(2,i,i) P_2_2(2,i,i)], [P_1(3,i,i) P_2_2(3,i,i)], 'color', 'r');
scatter(P_2_2(1,i,i), P_2_2(2,i,i))
% Set axis limits for consistency in all plots, show grid
axis([-2 2 -2 2])
grid on
% Hold off is good practice to avoid later accidental plotting on same axes
hold off
% Draw from the buffer
drawnow
end
you can save(if you want) this animation with getFrame function and play it with movie function
and another function may helps you is comet.