# How to stop rounding values when i use array?

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Alper Yasin on 7 Apr 2021 at 13:16
Commented: Alper Yasin on 7 Apr 2021 at 13:30
Hello everyone,
clear; clc;
syms f(y,t); %sym func
h = 0.1; %step size
ti = 0; %initial value
yi = 1; %value at ti = 0
f(t,y) = (1+2*t)*sqrt(y); %dif equation
for ti=[0:h:0.9] % t[0,1] condition with step size
k1 = f(ti,yi); %formula
k2 = vpa(f(ti+((1/2)*h),yi+((1/2)*k1*h))); %formula
k3 = vpa(f(ti+((1/2)*h),yi+((1/2)*k2*h))); %formula
k4 = vpa(f(ti+h,yi+k3*h)); %formula
c = ti+h; %trying to make it equal to another step
c = yi + ((1/6)*(k1 + 2*k2 + 2*k3 +k4)*h); %formula
ti = ti+h; % for calculating one step forward
yi = c %my values
end
This is my code. When i run this code i get these values which is alright for me.
yi = 1.113024864238065836914069386071
yi = 1.2543996857913360546038612123358
yi = 1.4280244537263716534345718377563
yi = 1.6383991563454554525623395070174
yi = 1.8906237821755359512988676861658
yi = 2.1903983207422986759010819641543
yi = 2.5440227630548922996833947540414
yi = 2.9583971018166219626153507261848
yi = 3.4410213314236507023824643153582
yi = 3.9999954478254578455556866889108
But when i use an array to plot these values. It automatically rounds them to closest value which is not alright for me cuz i need to plot the error as well. How can i solve this
Code with array:
clear; clc;
syms f(y,t); %sym func
h = 0.1; %step size
ti = 0; %initial value
yi = 1; %value at ti = 0
f(t,y) = (1+2*t)*sqrt(y); %dif equation
a = [];
b = 1;
for ti=[0:h:0.9] % t[0,1] condition with step size
k1 = f(ti,yi); %formula
k2 = vpa(f(ti+((1/2)*h),yi+((1/2)*k1*h))); %formula
k3 = vpa(f(ti+((1/2)*h),yi+((1/2)*k2*h))); %formula
k4 = vpa(f(ti+h,yi+k3*h)); %formula
c = ti+h; %trying to make it equal to another step
c = yi + ((1/6)*(k1 + 2*k2 + 2*k3 +k4)*h); %formula
ti = ti+h; % for calculating one step forward
yi = c %my values
a(b)=c
b = b+1;
end
plot(a,"r*")
a = 1.1130 1.2544 1.4280 1.6384 1.8906 2.1904 2.5440 2.9584 3.4410 4.0000
i know it is not a big problem one of them is 3.99999 other one is 4.0000 but i would like to know how to solve this.

Cris LaPierre on 7 Apr 2021 at 13:25
By default, MATLAB only displays 4 decimal places. This does not change the actual value. It's just for display. You can modify the display format using the format function.
a = 1.113024864238066
a = 1.1130
format long
a
a =
1.113024864238066
Alper Yasin on 7 Apr 2021 at 13:30
Thank you so much!

David Hill on 7 Apr 2021 at 13:26
The values in your array (a) are not rounded, they are only rounded in the display of them. To see the actual values, change format to long.
display(a);
format long;
display(a);
Alper Yasin on 7 Apr 2021 at 13:30
Thank you so much!

R2021a

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