Euler's Equation for Dummies

Question

Roddy 2013-10-1

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/88818-euler-s-equation-for-dummies

评论： Roddy 2013-10-1

I have never used Matlab before and I was given these 2 scripts:

function yprime = f_outline(t,y)
%This function evaluates yprime for use in Euler's method.  Use the 
% subfunctions p and t to calculate yprime.
% Note: This code will not work!  You have to edit it for the purposes of
% the lab
yprime = ;
function payment = p(t,y)
payment = 
function rate = r(t)
rate = ;

and

%Euler's Method
% Note: This code will not work!  It has holes that must be filled in.
clear all;
n = %number of steps
y = zeros(1,n); % Create a vector for the y values which will be calculated
y(1) = %initial value of y;
t(1) = 0;
%This loop computes one step of Euler's method each iteration
% Use f_outline.m to help compute each value of y.
for i = 2:n
    t(i) = i*%step size;
    y(i) = ;
end
plot(t,y)

My payment is 8000, my rate is 0.05, yprime=r*y*exp(r*t/(12*p))-12*p, y(1)=300000 t(1)=1 and I have to use the f_outline for y(i) with a while function until y(i)=0. My final codes look like this:

function yprime = f_outline(t,y)
yprime = r*y*exp(r*t/(12*p))-12*p;
function payment = p(t,y)
payment = 8000;
function rate = r(t)
rate = 0.05 ;

and

%Euler's Method
clear all;
n = .01
y = zeros(1,n); % Create a vector for the y values which will be calculated
y(1) = 300000
t(1) = 0;
%This loop computes one step of Euler's method each iteration
% Use f_outline.m to help compute each value of y.
while y(i)>0
for i = 2:n
    t(i) = i*n
    y(i) = f_outline(t(i),y(i))
end
end
plot(t,y)

but I keep getting this error:

lab1_euler_outline

n =
    0.0100
Warning: Size input contains non-integer values. This will error in a future release. Use FLOOR to convert to integer values. 
> In lab1_euler_outline at 4 
y =
      300000
Subscript indices must either be real positive integers or logicals.
Error in lab1_euler_outline (line 11)
while y(i)>0

Any help would be GREATLY appreciated.

Roddy

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Answer 1

A Jenkins 2013-10-1

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/88818-euler-s-equation-for-dummies#answer_98392

在 MATLAB Online 中打开

You have the statement

while y(i)>0

before the loop where i is defined.

Perhaps add

i=1

before that?

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Roddy 2013-10-1

在 MATLAB Online 中打开

This did not work but it got me to think that adding the

while y(i)>0

statement into the for statement which did work. I don't get an error now but I still don't get a graph. But that is another problem for another day I guess. Haha. Thanks A Jenkins!

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