MATLAB: “if it possible to only keep the value of the last two iterations”

matlab too slow

My simulation is running too slow because is keeping too many data. So, because I am using a double integrator, I would like to know if someone knows how to keep data from the last two iteration (i-1) and i in each loop. Thanks!

Best Answer

Seems fairly trivial, just store the results in a 1x2 cell array.

A=cell(1,2);
for i=1:10
    A{1}=A{2};
    A{2}=i 
end

A{1} stores the previous results (i-1) and A{2} stores the current results, i.

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MATLAB: Plotting two variables from a loop

% Constants
g=9.81;
m=1.5;
A=0.028; 
Cd=0.8;
rho=1.225;
B=(rho*Cd*A)/2;
Dt=1e-6;
% Initial values
x=0;
y=6.4008; %21 ft
V=12.5;
alpha=90;
Vx=V*sind(alpha);
Vy=V*cosd(alpha);
t=0;
X = zeros([],1) ; 
Y = zeros([],1) ; 
for k=1:1e9
    
    if y<0
        break
    end
    
    ax= -(B/m)*(V*Vx);
    ay=(B/m)*(V*Vy)-g;
    x=x+Vx*Dt+0.5*ax*(Dt^2);
    y=y+Vy*Dt+0.5*ay*(Dt^2);
    Vx=Vx+ax*Dt;
    Vy=Vy+ay*Dt;
    V=sqrt((Vx^2)+(Vy^2));
    
    t=t+Dt;
    X(k) = x ;
    Y(k) = y ; 
end
plot(X,Y)

MATLAB: Undefined function ‘m’ for input arguments of type ‘double

You have a reference to m(j) in the subject line but there's no definition of a variable m in the function nor is it in the argument list. Hence, to Matlab the expression m(j) looks like a function which you don't have one of, either.

If (as I presume) it's intended to be an array of masses (given the comment on acceleration and bodies), then pass it as another argument.

Best Answer

Related Solutions

MATLAB: Plotting two variables from a loop

MATLAB: Undefined function ‘m’ for input arguments of type ‘double

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