truncate decimal numbers in matlab?

Here's one method to truncate d digits after the decimal.

val = 1.234567;
d = 4;
val_trunc = fix(val*10^d)/10^d

Result

val_trunc =

   1.2345

If you know that val is positive then floor() will work in place of fix().

Yet another option:

x = -3.141592653;
x_trun = x - rem(x,0.0001)

x_trun =

    -3.1415

Kudos to gnovice for the update.

In general, for n decimal places:

x_trun = x - rem(x,10^-n)

Truncating is like rounding if you subtract 5 from the decimal after the last you want to keep.

So, to truncate x to n decimal figures use

round(x - sign(x)*.5/10^n, n)

(Thanks to @gnovice for noticing the need of sign(x) in order to deal with negative numbers.)

For example,

format long
x = 3.141592653589793;
for n = 2:5
    result = round(x - sign(x)*.5/10^n, n);
    disp(result)
end

gives

   3.140000000000000
   3.141000000000000
   3.141500000000000
   3.141590000000000