How to truncate all the decimal places??

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

Answer 1

[Iain]

 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.

Answer 2

[Dishant Arora]

doc cast

cast your variable to int16/32/64 depending upon your requirement.

[Phoebe]

what effect does changing int8 to int16 or int32 please? If i try the following;

if ((int8(time/diagstep) * diagstep) == time)

       [xcounter] = ParticleCounterFun(x0, particleno)   
       diagcounter=diagcounter+1
   end
It still does not work??

[Dishant Arora]

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.

Answer 3

[Gabor]

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]

t = datetime('now')

t = datetime
   16-Aug-2021 23:34:27

dateshift(t, 'start', 'hour')

ans = datetime
   16-Aug-2021 23:00:00