MATLAB: How to display all decimal numbers for floating numbers

decimalfloating point numbersMATLAB

The task I have to perform is take 2 user input numbers that must be floating numbers and add them together. However, when I do this, it cuts off at 4 decimal places. How do I make it so that it displays all decimal numbers? Do I have to use something with %f? I cannot use the "format" command. I am relatively new to MATLab, so any help would be appreciated! Below is what I have so far.

Best Answer

Try this

fprintf('num1+num2 = %1.16g\n',adding_num1_and_num2)

Related Solutions

MATLAB: Where do all these digits come from

3.141592653589793115997963468544185161590576171875

is what is stored for pi -- just a little longer than you happened to display.

If you are using MATLAB on MS Windows, then the digits you see output after the 16th are either 0 or garbage that happens to be randomly in the buffer. For MATLAB on MS Windows, to see numbers accurately, you should use num2strexact from the File Exchange.

If you are using MATLAB on Linux, then historically after some point (I no longer recall the length), fprintf() would produce zeros instead of correct digits.

If you are using MATLAB on Mac, then it has always produced all of the correct digits.

The digits you see are the base 10 representation of the binary value that is stored.

>> num2hex(pi)
ans =
    '400921fb54442d18'
>> pi-hex2num('400921fb54442d17')
ans =
      4.44089209850063e-16
>> hex2num('400921fb54442d19')-pi
ans =
      4.44089209850063e-16

>> sym(hex2num('400921fb54442d18'),'d')
ans =
3.141592653589793115997963468544185161590576171875
>> sym(hex2num('400921fb54442d19'),'d')
ans =
3.141592653589793560087173318606801331043243408203125
>> vpa(sym(pi)) 
ans =
3.141592653589793238462643383279502884197169399375105820974944592307816406286209

Comparing, you can see that the '400921fb54442d18' version is a little too low, and the '400921fb54442d19' version is a little too high. The value that was used, '400921fb54442d18', was chosen as being closer to the infinitely precise version of pi than the next number '400921fb54442d19' is.

MATLAB: How to change the way MATLAB displays the significant digits of floating point numbers

The FORMAT function allows users to set the default display method for floating point numbers in MATLAB.

The options for format are:

       FORMAT                                Default. Same as SHORT.
       FORMAT SHORT                          Scaled fixed point format with 5 digits.
       FORMAT LONG                           Scaled fixed point format with 15 digits.
       FORMAT SHORT E                        Floating point format with 5 digits.
       FORMAT LONG E                         Floating point format with 15 digits.
       FORMAT SHORT G                        Best of fixed or floating point format with 5 digits.
       FORMAT LONG G                         Best of fixed or floating point format with 15 digits.
       FORMAT HEX                            Hexadecimal format.
       FORMAT +                              The symbols +, - and blank are printed for positive,
                                             negative and zero elements.  Imaginary parts are ignored.
       FORMAT BANK                           Fixed format for dollars and cents.
       FORMAT RAT                            Approximation by ratio of small integers.
     Spacing:
       FORMAT COMPACT                        Suppress extra line-feeds.
       FORMAT LOOSE                          Puts the extra line-feeds back in.

For more information you should see the FORMAT documentation, accessible from MATLAB with the following command:

doc format

Here is a quick example:

>> format short
>> pi
ans =
      3.1416
>> format long
>> pi
ans =
     3.14159265358979

Currently, it is not possible to specify your own precision in MATLAB. A suggested work-around to this issue would be to use the CEIL and FLOOR functions, in combination with multiplication by magnitudes of 10, to round off to a particular precision.

For example, if you have a variable x = 3.1416, to obtain only three significant digits, you should do the following:

format short
x=pi
xtemp=x*1000
xtempt=ceil(xtemp)
x=xtempt/1000

Best Answer

Related Solutions

MATLAB: Where do all these digits come from

MATLAB: How to change the way MATLAB displays the significant digits of floating point numbers

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