I'm writing data to an output text file using the fprintf
command in Matlab. How to write a number to the output file, for instance, 1.12345678e-001
, with three digits in the exponent ?
formatSpec = '%1.8e\n';
gives 1.12345678e-01
, not the desired result!
There's a similar question here https://se.mathworks.com/matlabcentral/answers/100772-how-do-i-use-fprintf-to-write-numbers-in-exponential-notation-of-variable-exponent-digits-on-a-windo
But following the instructions given there didn't solve the problem!
You can use this non-regex method:
num = 0.112345678
pow = floor(log10(abs(num)));
sprintf('%.8fe%+.3d', num/10^pow, pow)
ans =
1.12345678e-001
For multiple inputs use this:
num= [.123 .456 .789];
pow = floor(log10(abs(num)));
sprintf('%.8fe%+.3d ', [num./10.^pow; pow])
Not sure if this falls under the category of solution or work-around , but here it goes:
x = .123e25; % example number
formatSpec = '%1.8e\n'; % format specification
s = sprintf(formatSpec, x); % "normal" sprintf
pat = '(?<=e)[+-]\d+'; % regex pattern to detect exponent
s = regexprep(s, pat, sprintf('%+04i', str2double(regexp(s, pat ,'match')))); % zero-pad
It uses regular expressions to identify the exponent substring and replace it with the exponent zero-padded to three digits. Positive exponents include a plus sign, as with fprintf
.
This isn't the cleanest answer but you could do something like this. Basic steps are write as is, get the exponent with a regexp, re-write that portion, and replace.
formatSpec = '%1.8e'
tempStr = sprintf(formatSpec,1.12345678e-1);
oldExp = regexp(tempStr,'e[+-]([0-9]+)$','tokens');
newExp = num2str(str2double(oldExp{1}{1}),'%03d');
fixedStr = regexprep(tempStr,[oldExp{1}{1} '$'],newExp)
This outputs:
fixedStr =
1.12345678e-001
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