# How to truncate all the decimal places??

38 views (last 30 days)
Phoebe on 25 Feb 2014
Commented: Walter Roberson on 16 Aug 2021
I am working on a code that loops over time and have been told that I am at this time "rounding the time to the nearest whole number. This is wrong. You need to truncate all the decimal places." I am unsure exactly what this means and how to implement so any would be appreciated. A relevant extract of my code is below;
time=0;
dt=0.01; %Define time step
tfinal=40;
diagstep=10; %diagnostic time step
diagcounter=0;
while time<tfinal
time=time+dt;
if (round(time/diagstep * diagstep) == time)
[xcounter] = ParticleCounterFun(x0, particleno)
diagcounter=diagcounter+1
end
end
%%xcounter function file is;
function [ xcounter ] = ParticleCounterFun( x0, particleno )
%Initialise counters used in E field diagnostics
counter01=0;
counter12=0;
counter23=0;
counter34=0;
counter45=0;
for np=1:particleno
if (0<=x0(np) & x0(np)<1)
counter01=counter01+1;
end
if (1<=x0(np) & x0(np)<2)
counter12=counter12+1;
end
if (2<=x0(np) & x0(np)<3)
counter23=counter23+1;
end
if (3<=x0(np) & x0(np)<4)
counter34=counter34+1;
end
if (4<=x0(np) & x0(np)<5)
counter45=counter45+1;
end
end
xcounter=[counter01 counter12 counter23 counter34 counter45]
end
It is in the condition for the IF statement that i must 'truncate all decimal places' and not just round to nearest whole number so if anyone could help me on this!
Thanks!
Phoebe

Iain on 25 Feb 2014
fix(time) rounds time towards 0, so it gets rid of the decimal places. (truncates numerically)
str = num2str(time); truncated = str(1); this takes the 1st character when the number is expressed as a string (truncates textually - you will need to change this to do it properly)
It looks like you wanted to round to something other than the nearest integer, but got it wrong: If you want rid of all but the 1st decimal place, then you want, fix(time*10)/10 if you want rounded down to the nearest 10, fix(time/10)*10.

Dishant Arora on 25 Feb 2014
doc cast
##### 2 CommentsShowHide 1 older comment
Dishant Arora on 27 Feb 2014
what is it that you exactly want to do?? probably you need to change diagnostic step to 100.
round(time*100)/100==dt
or use fix as Iain said.

Gabor on 16 Aug 2021
Edited: Gabor on 16 Aug 2021
fix(1.12) -> remove decimals -> result: 1
fix(23.858457) -> remove decimals -> result: 23
For datetime comparison:
datenum(datetime('now','Format','d-MMM-y')) -> 738385.03
fix(datenum(datetime('now','Format','d-MMM-y'))) -> 738385.00
Took me 20 minutes to find the answer to this simple question, I hope I saved some time for you!
Walter Roberson on 16 Aug 2021
t = datetime('now')
t = datetime
16-Aug-2021 23:34:27
dateshift(t, 'start', 'hour')
ans = datetime
16-Aug-2021 23:00:00