Format Number (exponential notation)

I have a code and a result is the variabile: T= 5.6789e-05

I want use a function for change the exponential notation from e-05 to e-6 and print the value in a graph.

Correct value T= 56.789e-06

Help me

sprintf('time T= %3.3e\n',T)

Answer 1

[Walter Roberson]

You will not be able to do this directly. sprintf and related do not offer any control over where the decimal is put.

You can use log10 to probe the power of 10 for the value, such as -5. Divide by that power minus 1 to get a value with two leading decimals. Format that. Add on sprintf('e%d') the power minus 1

[Matteo Peruzzi]

thankyou Walter for your fast answer.

interesting metode but I don't understand what I have to write ;)

If I have a general variable T=A*10^(x)

where A and x are unknows

(for example T=5.6789e-05 or T=458.45e-04 ...)

I want probe the power of 10 with log10

From math we know:

log10(T) = log10( A*10^(x) ) = log10(A)+log10( 10^(x) ) = log10(A)+log10(10^(x))

log10(T)=log10(A)+x

and x=log10(T)-log10(A)

or x=log10(T/A)

x(the power of 10) is different to only log10(T)

in other way

log10(5.6789e-05) is not -5

Maybe you have other ideas

thankyou

[Walter Roberson]

X=5.6789e-05; D=floor(log10(5.6789e-05))-1; X/10^D

gives 56.789.

[Matteo Peruzzi]

really thankyou.

I didn't know floor comand, I m a student and I'm writting my thesis

Now in Command Windows (display) I obtain correct result (56.789e-06)

But in workspace the variable is again (5.6789e-05) and when I report the result in a graph legend it remain 5.6789e-05.

Do you have any ideas?

Part of my code is:

%EXAMPLE WITH t2
x=floor(log10(t2))-1
t2=t2/10^(-6-x)


legend([c b m g v ],   {    [sprintf('tA-O1 = 0.5* T = Ti= %3.3e\n', Ti)], ...
                            [sprintf('tB-tA = T= %3.3e\n', T) ], ...
                            [sprintf('front time T/0.6 = T1 = %3.3e\n', T1)], ...
                            [sprintf('time to half value t2=  %3.3e\n', t2)], ...
                            [sprintf('peak value Vpp= %.4g\n', Vpp)],  });

[Walter Roberson]

X=5.6789e-05;
D=floor(log10(5.6789e-05))-1;
t2S = sprintf('time to half time t2=%.4fe%d', X/10^D, D) ;

and use the variable in constructing the legend.

[Matteo Peruzzi]

I have change anything.....and work fine ;)

GOOD!!! Really thankyou

Now Italy is not a good place. 6000 dead in two weeks. Take care and rest at home.