MATLAB is giving me 0's instead of really small numbers
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Nicholas Morris
am 17 Aug. 2021
Kommentiert: Walter Roberson
am 17 Apr. 2023
I don't have code to share, but MATLAB is outputing 0's instead carrying through small numbers. When I change the command window to format long, the calculation show non zero. However, when my code runs it is carrying these zeros through my calculations.
>> Calculation
ans =
0.0
>> Format long
>> Calculation
ans =
8.425293911978570e-07
How do I make matlab keep the small numbers?
2 Kommentare
Steven Lord
am 18 Aug. 2021
Can you show us a small segment of the code that appears to return 0's instead of the small numbers you expected?
How small is "really small" in this context? Smaller than realmin?
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Walter Roberson
am 17 Aug. 2021
MATLAB is keeping the small numbers throughout your calculation.
I recommend that you put
format long g
at the top of your code and run again.
3 Kommentare
Walter Roberson
am 18 Aug. 2021
Your code might be zeroing the entire array at each step.
But as well, "format long g" does not affect the variable browser. There is a drop-down above the variable name that can select the format for the variable browser; personally though I recommend setting Preferences -> Variables -> Default Array Format to "long g", which controls the default format for the variable browser.
vikas singh
am 12 Mär. 2023
Bearbeitet: Walter Roberson
am 12 Mär. 2023
I have written a code and it is giving me H3 and z2 zero. i dont know what is the problem.
clc;
clear all;
close all;
l=10000;
x=0:100:l;
t=[0;1;5;10;15;20;25];
H=30;
alpha=0.00384
Mu=2.8e-1;
D=31;
k=0.01132;
k1=l/H;
for n=1:100
a=2*H;
b=(1-(-1)^n*exp(-k*l))/((n*pi+(k^2*l^2)/(n*pi)));
c=1/(n*pi);
Cn(n)=a*(b-c);
end
s=0;
for n=1:100
d= sin(n*pi*x/l);
q= exp((-n^2*pi^2*t)/(Mu^2*l));
aa=Cn(n).*d.*q;
s=s+aa;
bb=(2*alpha*Mu^2*l^2)/(n*pi)^3;
s2=bb.*(1-q).*d;
end
J=(H+alpha*t).*x/l;
J1=alpha*t;
z1=s-s2-J+J1;
for n=1:100
syms X T
disp(n)
H0=(Cn(n)/(D-H)).*sin(n*pi*X).*exp(-n^2*pi^2*T/Mu)+(bb/(D-H)).*(1-exp(-n^2*pi^2*T/Mu)).*sin(n*pi*X) +(H/(D-H)+alpha*T*Mu*l/(D-H))*X+(H-alpha*T*Mu*l)/(D-H);
y=diff(H0*diff(H0,X),X);
Q=int(y*sin(n*pi*X),X,0,1);
P=int(Q*exp(n^2*pi^2*T/Mu),T,0,T);
Hn=-2*P/(exp(n^2*pi^2*T/Mu));
H1=Hn.*sin(n*pi*X);
for i=1:size(t,1)
H2=subs(H1,T,t/(Mu*l));
end
format long g
H3=subs(H2,X,x/l)
end
z2=double(((D-H)^2).*H3/l)
22 Kommentare
Walter Roberson
am 17 Apr. 2023
Take the output of q4s in the code I show and do
output = subs(q4s, n, 1:100);
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