Varying Variables within a Function
显示 更早的评论
The code that I currently have works perfectly for the variables that I have already assigned as constants.
%Setting the time interval in seconds
tspan = [0 20];
%Using the ODE Function
[t,x] = ode45(@Cart,tspan,[5 0]);
%Plotting the graph with a legend
plot(t,x(:,1),'DisplayName','Position'); hold on;
plot(t,x(:,2),'DisplayName','Velocity');
xlabel('Time'); ylabel('X-Values');
legend
%Writing out the function
function output = Cart(t,x)
m=2; %mass
b = 1.3; %damping
k = 20; %spring constant
x1prime = x(2);
x2prime = (-k*x(1)-b*x(2))/m;
output = [x1prime; x2prime];
end
Thank you for your time and help!
3 个评论
Walter Roberson
2020-11-14
Sam Zavala:
If you feel that your question is unclear, then since you are the author of the question, instead of flagging the question and hoping that a moderator will kindly take the time to figure out what you really meant and re-write the question to be better explained, then you should be spending the time to explain the question better yourself. You are the person who knows best what you need; you should not expect that someone else will spend the time making your question more clear.
Sam Zavala
2020-11-14
采纳的回答
%Setting the time interval in seconds
tspan = [0 20];
%% Define the values to iterate through
m = [2, 3, 4, 5, 6]; %mass --> vector with varied masses
b = [1.3, 1.5, 2, 2.5, 3]; %damping --> vector with varied damp
k = [20, 30, 40, 50, 60]; %spring constant
%% original values without vary
%Using the ODE Function
[t,x] = ode45(@(t,x)Cart(t,x,m(1),b(1),k(1)),tspan,[5 0]);
%Plotting the graph with a legend
subplot(2,2,1)
plot(t,x(:,1),'b','DisplayName','Position');
hold on;
plot(t,x(:,2),'r','DisplayName','Velocity');
xlabel('Time');
ylabel('X-Values');
legend('boxoff')
%% vary m
% Preallocate cell array for results of 5 runs with varying m
X_m = cell(numel(m),1);
% loop through the masses
% Note that the non varied values are the first entry in the vectors for
% m, b and k
for ii = 1:numel(m)
[t,x] = ode45(@(t,x)Cart(t,x,m(ii),b(1),k(1)),tspan,[5 0]);
X_m{ii} = [t, x];
end
% Plot the different values
subplot(2,2,2)
hold on;
for ii = 1:numel(m)
plot(X_m{ii,1}(:,1),X_m{ii,1}(:,2),'b');
plot(X_m{ii,1}(:,1),X_m{ii,1}(:,3),'r');
end
hold off
xlabel('Time'); ylabel('X-Values (m varied)');
legend({'Position','Velocity'})
legend('boxoff')
%% vary b
% Preallocate cell array for results of 5 runs with varying b
X_b = cell(numel(b),1);
% loop through the masses
for ii = 1:numel(b)
[t,x] = ode45(@(t,x)Cart(t,x,m(1),b(ii),k(1)),tspan,[5 0]);
X_b{ii} = [t x];
end
% Plot the different values
subplot(2,2,3)
hold on;
for ii = 1:numel(b)
plot(X_b{ii,1}(:,1),X_b{ii,1}(:,2),'b');
plot(X_b{ii,1}(:,1),X_b{ii,1}(:,3),'r');
end
hold off
xlabel('Time'); ylabel('X-Values (b varied)');
legend({'Position','Velocity'})
legend('boxoff')
%% vary k
% Preallocate cell array for results of 5 runs with varying k
X_k = cell(numel(k),1);
% loop through the masses
for ii = 1:numel(k)
[t,x] = ode45(@(t,x)Cart(t,x,m(1),b(1),k(ii)),tspan,[5 0]);
X_k{ii} = [t x];
end
% Plot the different values
subplot(2,2,4)
hold on;
for ii = 1:numel(k)
plot(X_k{ii,1}(:,1),X_k{ii,1}(:,2),'b');
plot(X_k{ii,1}(:,1),X_k{ii,1}(:,3),'r');
end
hold off
xlabel('Time'); ylabel('X-Values (k varied)');
legend({'Position','Velocity'})
legend('boxoff')
%% Writing out the function
function output = Cart(~,x,m,b,k)
x1prime = x(2);
x2prime = (-k.*x(1)-b.*x(2))./m;
output = [x1prime; x2prime];
end
2 个评论
Stephan
2020-11-9
The usual way is to try to avoid for loops and work with vectorization. This is nearly always the most efficient way.
But this
1) does not work always and
2) if it would work you still need to understand the code one year later.
So it may be possible, but there is also a trade off between understanding what the code does and being efficient.
Sam Zavala
2020-11-10
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