Sig figs on the rand function

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Spaceman 2024-3-20

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https://ww2.mathworks.cn/matlabcentral/answers/2096561-sig-figs-on-the-rand-function

评论： Spaceman 2024-3-20

Just another general question here, is there a reason the rand function has 6 sig figs? i.e. 12.3456

Is there a way to change this so there are more or less post decimal? Or is this just how MATLAB handles this function, generally.

Thank you in advance!

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Answer 1

Chunru 2024-3-20

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在 MATLAB Online 中打开

==> Just another general question here, is there a reason the rand function has 6 sig figs? i.e. 12.3456

rand function (by defaut) has "double" type, which means it is represented internally by 64bits, precision of up to 15 digits.

MATLAB has a default display format, which is "short" and has 4 digits after decimal point (Note: this is only for display, internal computations are based on double).

==>Is there a way to change this so there are more or less post decimal? Or is this just how MATLAB handles this function, generally.

Use format long to display data with more digits after decimal point (doc format for more details)

a = rand();         % internally stored as double
a                   % default (4 digits after dp)
a = 0.0083
format long         % (15 digits after dp)
a
a = 
   0.008251124809451

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Chunru 2024-3-20

在 MATLAB Online 中打开

% format long?
format long
grade=rand(1,49)*(100-20)+20; % could also do randi([20 100],1,49);
% format long?
grade_avg=mean(grade);
grade_avg
grade_avg = 
  61.084787400165922
% Use fprintf for more control of the format
%fprintf('The average grade is %1.0f \n',grade_avg)
fprintf('The average grade is %0.10f \n',grade_avg)  % 10 digits after dp
The average grade is 61.0847874002 
if grade_avg>=60
    disp('passing average')
else
    disp('failing average')
end
passing average
format default      % revert to default
grade_avg
grade_avg = 61.0848