Displaying exponential notation with num2str?

I have a value that I want to display within a textbox in a figure. The value hoewer needs to be in exponential notation.

Example:

lambda = 2.4321;
vD = 3.2e5;

fighandle = figure(1);
fighandle.Color = [1,1,1];
fighandle.Position = [10,50,600,400];
fighandle.Name = 'Test';
xlabel('t [min]','FontSize',12,'Interpreter','latex');
ylabel('Temperatur [$^\circ$C]','FontSize',12,'Interpreter','latex');

annotation('textbox', [0.66, 0.15, 0.1, 0.1], ...
    'String', {['$\lambda$ = ' num2str(round(lambda,3),'%.3f') ' W/mK'], ...
    ['$v_D$ = ' num2str(round(vD,1),'%.1f') ' m/s']}, ...
    'BackgroundColor', 'White', ...
    'Interpreter','latex');

The result looks like this:

But i want the variable b to look like this:

Any ideas? Thank you very much for the help!

Answer 1

[Star Strider]

I wrote a little utility program to do that sort of thing a few years ago.

Try this —

Q1 = [-pi*1000; 0; pi*100];
expstr = @(x) [x(:).*10.^ceil(-log10(abs(x(:)+(x==0)))) floor(log10(abs(x(:)+(x==0))))];       % Updated: 2021 05 04
Result = sprintf('%+.4fe%+04d\n', expstr(Q1).')

Result = 
    '-3.1416e+003
     +0.0000e+000
     +3.1416e+002
     '

V = expstr(Q1)

V = 3×2

-3.1416 3.0000 0 0 3.1416 2.0000

Create the sprintf format string (that I use here) to give the result you want.

.

[Michael]

Thank you very much! That did, what I was looking for :)

I implemented it this way within the annotation textbox:

vD_expstr = expstr(vD);

% ...

['$v_D$ = ' num2str(round(vD_expstr(1),1),'%.1f') ' $\cdot$ 10' num2str(vD_expstr(2),'$^{%.0f}$') ' m/s']

[Star Strider]

As always, my pleasure!

That will work, since num2str allows format strings, although sprintf might be an easier way to implement it.

I created ‘expstr’ precisely for the purpose you’re using it!

Answer 2

[Steven Lord]

Another function that might be of interest to you is formattedDisplayText, if you want to capture how the variable would be displayed in MATLAB using a certain display format.

x = pi

x = 3.1416

y1 = formattedDisplayText(x)

y1 = 
    "    3.1416
     "

format longeng
x

x = 
    3.14159265358979e+000

y2 = formattedDisplayText(x)

y2 = 
    "    3.14159265358979e+000
     "