If command does not work correctly.

Hello, I am preparing a gui for some formulas.

I want to prefix the formula results like mili-micro.

For example

Let the result be 0.0025V(voltage)

I want to write 2.5mV or 2500uV in the result section

For this, I want to get an integer by multiplying the resulting number by 10.

I will act according to how many times the multiplication is made.

For example

Let the answer be 0.026V, the number obtained from 3 multiplications is 26.

Since it is the result of 3 multiplications, the prefix will be "mili"

To understand where the multiplication stops, I check whether the number is an integer after each multiplication.

I did some research for this.

floor(V)==V

I will check the number this way.

There are some problems in the code

for loop doesn't stop where it should

I=input("enter number");   
disp(I)
if I<1
    for multiplication = 1:100
        I=I*10 
        if floor(I)==I
            break;
        end
    end
end              

For example, I will enter two numbers

enter number 0.159
159.000000000000e-003


I =

1.59000000000000e+000


I =

15.9000000000000e+000


I =

159.000000000000e+000

>> 

It worked correctly for that number and stopped when the if condition was true,when it was an integer.

enter number 0.234
234.000000000000e-003


I =

2.34000000000000e+000


I =

23.4000000000000e+000


I =

234.000000000000e+000 


I =

2.34000000000000e+003


I =

23.4000000000000e+003


I =

234.000000000000e+003


I =

2.34000000000000e+006


I =

23.4000000000000e+006


I =

234.000000000000e+006


I =

2.34000000000000e+009


I =

23.4000000000000e+009


I =

234.000000000000e+009


I =

2.34000000000000e+012


I =

23.4000000000000e+012


I =

234.000000000000e+012


I =

2.34000000000000e+015


I =

23.4000000000000e+015

but in this example, even though it was an integer (even though the if condition was met), the for loop did not stop.

Can you help me I'm very confused

[Stephen23]

"I want to prefix the formula results like mili-micro"

The simple approach is to download my FEX submission NUM2SIP():

https://www.mathworks.com/matlabcentral/fileexchange/33174-number-to-scientific-prefix

and use it like this, with the examples from your question:

[num2sip(0.0025),'V']

ans = '2.5 mV'

[num2sip(0.026),'V']

ans = '26 mV'

and with the examples from your comment here:

[num2sip(32000000),'Hz']

ans = '32 MHz'

[num2sip(25000),'Ω']

ans = '25 kΩ'

[num2sip(0.0000035),'F']

ans = '3.5 µF'

Note that the space is required by the SI standard.

Most users underestimate the level of detail required to perform provide this conversion in a robust way**. Given that I have already created this function and tested it on hundeds of test-cases (included on FEX), why reinvent the wheel?

** I have systematically tested all FEX submissions (that I could find) that claim to make this conversion. Most of them are buggy (usually with very similar oversight e.g. regarding how to handle significant figures correctly and how to round up to the next prefix when required), very few of them actually gave the correct output.

Answer 1

[Dyuman Joshi]

Welcome to the world of floating point numbers, where not all numbers can be represented exactly in binary form.

0.234 is not exactly stored as 0.234 -

I=0.234; %input("enter number");   
disp(I)

    0.2340

%stored value upto 42 digits after decimal
fprintf('%0.42f', I)

0.234000000000000013544720900426909793168306

Let's check the value of I (upto 20 digits after decimal), with for a few iterations -

if I<1
    for multiplication = 1:5%100
        I=I*10;
        fprintf('Iteration %d\nI = %0.20f\nfloor(I) = %0.20f\n\n', multiplication, I, floor(I))
        if floor(I)==I
            break;
        end
    end
end

Iteration 1
I = 2.34000000000000030198
floor(I) = 2.00000000000000000000

Iteration 2
I = 23.40000000000000213163
floor(I) = 23.00000000000000000000

Iteration 3
I = 234.00000000000002842171
floor(I) = 234.00000000000000000000

Iteration 4
I = 2340.00000000000045474735
floor(I) = 2340.00000000000000000000

Iteration 5
I = 23400.00000000000363797881
floor(I) = 23400.00000000000000000000

As you can see, I is not equal to floor(I), that's why the loop does not break.

When comparing floating point numbers, the best practice is to use a tolerance -

I = 0.234;
tol = 1e-3;
if I<1
    for multiplication = 1:5%100
        I=I*10;
        fprintf('Iteration %d\nI = %0.20f\nfloor(I) = %0.20f\n\n', multiplication, I, floor(I))
        if abs(floor(I)-I)<tol
            break;
        end
    end
end

Iteration 1
I = 2.34000000000000030198
floor(I) = 2.00000000000000000000

Iteration 2
I = 23.40000000000000213163
floor(I) = 23.00000000000000000000

Iteration 3
I = 234.00000000000002842171
floor(I) = 234.00000000000000000000

Now you can observe that the loop has been terminated after 3 iterations, as initially expected.

Note - The choice of tolerance depends on requirement and other factors.

P.S - If you want to see the exact conversion of a number (to string format) based on IEEE floating point number system, you can utilize this FEX submission by James Tursa - https://in.mathworks.com/matlabcentral/fileexchange/22239-num2strexact-exact-version-of-num2str?s_tid=prof_contriblnk

[Bahadir Guven]

Thank you very much for your help but I still cannot provide all the numbers.

I think the tolerance value is not valid for the entire system.

When I select another tolerance value, the other values are not correct

For example

initial value 0.0003

final value 3.0000e+16

[Stephen23]

"I think the tolerance value is not valid for the entire system."

That is quite possible: there is no tolerance value that is suitable for everything.

As Dyuman Joshi wrote "The choice of tolerance depends on requirement and other factors", i.e. you need to adjust the tolerance to suit your task and data values.

[Dyuman Joshi]

@Bahadir Guven, is the objective here just to convert the values to be expressed as milli-volts or micro-volts?

Also, is it to use any one of them for all, or choose between them based on some criteria/logic?

[Bahadir Guven]

is the objective here just to convert the values to be expressed as milli-volts or micro-volts?

Yes, as you said. I want to this.

Do you have any ideas?

[Dyuman Joshi]

Why not multiply the data with 10^3 or 10^6?

[Bahadir Guven]

I misunderstood, I want you to ensure that it shows engineering notion for all results.

For example

32MHz, 25k, and 3.5µF would be 32.000,000 hertz, 25.000 ohms and 0.0000035 farads.

I'm trying to make submultiple first .Just "mili or micro" is example.

[Dyuman Joshi]

"32MHz, 25k, and 3.5µF would be 32.000,000 hertz, 25.000 ohms and 0.0000035 farads."

Alright.

But what would be the input corresponding to these cases?

[Bahadir Guven]

it can be any value between 10e-15 - 10e+15

[Stephen23]

"it can be any value between 10e-15 - 10e+15"

My function NUM2SIP() already copes with all real values from +REALMAX to -REALMAX, includes the SI prefixes added in 2022, and is tested on hundreds of testcases. Why reinvent the wheel?

[Dyuman Joshi]

Let me clarify - the input will be of the form of - 32MHz, 25k, and 3.5µF, and you want the output to be of the form - '32.000,000 hertz, 25.000 ohms and 0.0000035 farads' (diregarding the units, of course)?

Or is it the opposite of what I mentioned above?