MATLAB: I am getting an asterisk as the output for the script

format ratfprintfoutputrat

I am trying to create a script to perform second order ODE's in a user friendly environment. For some reason when I use the fprintf i cannot get it to print out the value however the value is stored, it just prints a "*". I want my answers to be in fractions, it works except when it is a large fraction. I was trying to perform the complex root ODE with coefficients a=4, b=24, c=37 and IVP of y(pi)=1 dydt(pi)=0

I cant figure out how to add my code correctly but i have attached the m file

Best Answer

rats() returns * for any value from 10^13 and larger, or any value from -10^12 and less (more negative), or any non-zero value sufficiently value sufficiently close to 0, or even some values as large as 0.000999 (but works for 0.0009999)

I suggest that instead of calling rats, you call the two-output version of rat() and format the pieces.

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MATLAB: How to drop last N round-off error digits

Hi Ilya,

if you are happy with an output, then use fprintf:

a=sqrt(pi);
fprintf('a = %.14g\n', a)
a = 1.7724538509055

Otherwise: use e.g. eps to find the roundoff digit.

a = sqrt(pi);
e = eps(a);
% how many decimal digits it this?
digits = floor(-log10(e));
% cut off the last two
digits = digits - 2;
% round to this digit
aRound = round(a*10^digits) / (10^digits)
aRound =
 1.772453850905500

Titus

MATLAB: Using fprintf with matrices with rational entries

Have to switch to string representation to do so or use the related rat function instead...

[n d]=rat(x);
for i=1:size(x,1)
  for j=1:size(x,2)
    if d(i,j)==1
      fprintf('%5d',n(i,j))
    else
      fprintf('%5d/%5d',n(i,j), d(i,j))
    end
  end
  fprintf('\n')
end

For rats

ra=arrayfun(@rats,x,'uniformoutput',0);
for i=1:size(x,1)
  for j=1:size(x,2)
    fprintf('%8s',char(strtrim(ra(i,j))))
  end
fprintf('\n')
end

Best Answer

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MATLAB: How to drop last N round-off error digits

MATLAB: Using fprintf with matrices with rational entries

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