How can I reduce the number of digits after the decimal point?

Matlab shows a number with 2 digits after the decimal point (e.g. 0.8100) in the Command Window, but when you open the variable it is 0.810000000000000. Do you know how I can cut those zeros off?

I do not want to show them in the Command Window (print, fprint or anything like that). I want to see just 2 digits after the decimal point when I open the variable in the Variables section.

Also, I have tried round(x*1000)/1000 and Format (short and bank), and they do not do what I want to!

I saw that someone else had the same problem a while ago ( here) but no one knew the correct answer!

Thanks.

Answer 1

[Stephen23]

To control how numbers are displayed in the Variable Viewer, you can set the format in the Preferences:

Home tab, in the Environment section, click Preferences. Select MATLAB > Variables.

https://www.mathworks.com/help/matlab/matlab_env/set-workspace-and-variable-preferences.html

[Milad Zarei]

Thanks Stephen. I tried that but still get the same answer!

[Stephen23]

I just tried several format options, and it works for me. For example, when I set it to rat, I get this:

and with short I get this:

Note that you will need to close and reopen the Variable Viewer to get the change.

[Milad Zarei]

You should double click on the values to see the actual values!! This is the value before and after the "double click" in the short format.

Before:

After:

[Stephen23]

That is MATLAB helpfully telling you how many digits of precision there are for that variable class. If you make your variable single you will see fewer digits.

It is an intentional design decision to show all of those digits.

Basically this is a case of "you can't please all people all of the time". So many beginners complain that MATLAB ate their digits: they are concerned that MATLAB reads or calculates with only five significant digit precision. When they see only five digits printed in the command window they panic. And so there is one easy way that MATLAB provides that shows all digits for any numeric variable: double click in the variable viewer. This is supposed to reassure people that their data is intact.

Summary: the Viewer is supposed to show all significant decimal digits for that class when double clicked.

PS: You could try the bank format (I know it is not double clicked):

PPS: How would this be useful anyway? What are you trying to do?

[Milad Zarei]

I have 2 different column matrices (A & B), but they have some mutual values at different rows! I use this piece of script to find the mutual values:

LC1 = A(1)-10;

LC2 = A(20)-10;

LC3 = A(end)-10;

LP1 = find(BB==LC1);

LP2 = find(BB==LC2);

LP3 = find(BB==LC3);

I do need to subtract 10 of those values! And that's where the problem pops up! Since the values from the A and B matrices are not exactly the same (to the 15 digits after the decimal point), the "find" command returns "Empty matrix: 0-by-1". I checked the values on the Viewer, and they are slightly different (e.g. A(1)-10 = 0.00000000001). So, the find command cannot find any values from the B matrix! But if I can reduce the precision, then it probably would work fine!

[Walter Roberson]

Changing how the data is displayed will not help you with this matter.

http://matlab.wikia.com/wiki/FAQ#Why_is_0.3_-_0.2_-_0.1_.28or_similar.29_not_equal_to_zero.3F

You should compare with a tolerance, perhaps using ismembertol()

[Stephen23]

@Milad Zarei: how numbers are displayed is totally irrelevant to how operations are performed on them. Changing how they are displayed does not change the number of digits of precision in the stored number. It just changes the display of that number.

As Walter Roberson says, you need to use a tolerance when comparing the numbers.

You might like to read this too: http://mywiki.wooledge.org/XyProblem

[Milad Zarei]

lol! That's me! Thanks :)

[Milad Zarei]

Walter Roberson, thank you for the response. I managed to got it worked! But I don't know how to accept your answer or vote for it!

[Walter Roberson]

Stephen answered the question you asked, so vote for that ;-)

[Neetesh Kumar Sharma]

its not working