Formating String Parameter Left of Decimal

In the following code, I want to create the str variable to read: Radius=100E-6 meter

However, I keep getting: Radius=1.00E-4 meter

I can't seem to force it to place more digits to the left of the decimal. How do I revise sprintf to produce the former instead of the latter?

a=100E-6;
str=sprintf('Radius=%3.0E meter,',a);

I know the answer is probably something simple, but I just can't seem to figure it out.

Thanks in advance,

M Ridzon

[Stephen23]

The standard C-based MATLAB command sprintf does not produce "engineering" exponents, it always produces exponents with one digit before the decimal point. You might like to read these (but don't use the first answer!):

https://www.mathworks.com/matlabcentral/answers/892-engineering-notation-printed-into-files

https://www.mathworks.com/matlabcentral/answers/62708-custom-output-of-the-fprintf

[Stephen23]

As an alternative you could download my FEX submission num2sip, which generates SI/metric prefixes:

>> num2sip(1.234e-4)
ans = 123.4 u

Following your example you could do something like this:

>> sprintf('Radius = %smeter',num2sip(1.234e-4,[],true))
ans = Radius = 123.4 micrometer

Note that unlike the accepted answer num2sip correctly returns the requested precision, regardless of the order of the number:

>> num2sip(1.4567e-4)
ans = 145.67 u
>> num2sip(1.4567e-5)
ans = 14.567 u
>> num2sip(1.4567e-6)
ans = 1.4567 u

Answer 1

[Star Strider]

I wrote a little utility function for my own purposes to do this a while ago:

engstr = @(x) [x*10.^(-3*floor(log10(abs(x))/3))  3*floor(log10(abs(x))/3)];    % Engineering Notation Mantissa & Exponent

x = 1E-4;
Result = sprintf('%3.0fE%-.0f', engstr(x))

Result =
    '100E-6'

Configure the sprintf format string to produce the output you want.

[Stephen23]

Note that this gives no control over the precision of the output, and will eat digits without warning:

>> engstr = @(x) [x*10.^(-3*floor(log10(abs(x))/3))  3*floor(log10(abs(x))/3)];
>> sprintf('%3.0fE%-.0f', engstr(1.4567e-4))
ans = 146E-6
>> sprintf('%3.0fE%-.0f', engstr(1.4567e-5))
ans =  15E-6
>> sprintf('%3.0fE%-.0f', engstr(1.4567e-6))
ans =   1E-6

[Matthew]

Wonderful! This works perfectly!

[Star Strider]

@Matthew —

As always, my pleasure!

Answer 2

[John D'Errico]

Personally, 100e-6 seems like a silly and confusing way to write the number 1e-4. And at some point in my educational career, I even spent some time as an engineer. What you are probably looking for is known as engineering notation.

format SHORTENG
a = 1e-4
a =
   100.0000e-006

So can you just display the number directly? I don't see a simple way to force sprintf to work, as it does not seem to include the engineering notation form as an option.

[Matthew]

Thanks for the input. I want to use str in a title command being used to generation a post-processing plot. E-6 notation makes sense in this problem since it clearly communicates that the radius is derived from the micrometer scale, but being reported in the meter scale. And thus it is very obvious to the person reading the plot. But it sounds like I'm unable to use this approach since engineering format isn't available. Oh well, I'll come up with plan B.

Thanks, M Ridzon

[John D'Errico]

Personally, I was surprised that sprintf did not offer engineering notation as an option. I suppose you could write a utility that worked like sprintf, but used engineering notation. It would take some amount of effort, that might not be worth the mental energy expended.