asking about command in matlab

what this command mean in details

Energy = 0.17+rand(1,1)*(0.19-0.17)

thanks

Answer 1

[the cyclist]

Are you willing to spend some time learning MATLAB? You will fully understand that line of code if you

• Watch the free, online MATLAB Onramp tutorial (maybe even just the first 30 minutes will be enough)
• Read even a little of the documentation for the rand function

Answer 2

[John D'Errico]

As much as I completely agree with @the cyclist, that you need to start to learn MATLAB, you also need to learn to take apart a line of code. That in itself is a skill you need to learn. And it applies to ANY programming language. You would start at the most basic element of the code, and then work out, based on the order of operations in the language you are using.

And in fact, if you just read the docs for rand, you will find that exact form of the expression discussed. (Not a command though.)

So first, start in the middle. What does rand(1,1) do?

help rand

 RAND Uniformly distributed pseudorandom numbers.
    R = RAND(N) returns an N-by-N matrix containing pseudorandom values drawn
    from the standard uniform distribution on the open interval(0,1).  RAND(M,N)
    or RAND([M,N]) returns an M-by-N matrix.  RAND(M,N,P,...) or
    RAND([M,N,P,...]) returns an M-by-N-by-P-by-... array.  RAND returns a
    scalar.  RAND(SIZE(A)) returns an array the same size as A.
 
    Note: The size inputs M, N, P, ... should be nonnegative integers.
    Negative integers are treated as 0.
 
    R = RAND(..., CLASSNAME) returns an array of uniform values of the 
    specified class. CLASSNAME can be 'double' or 'single'.
 
    R = RAND(..., 'like', Y) is an array of uniform values with the same
    data type and complexity (real or complex) as the numeric variable Y.
 
    The sequence of numbers produced by RAND is determined by the settings of
    the uniform random number generator that underlies RAND, RANDI, and RANDN.
    Control that shared random number generator using RNG.
 
    Examples:
 
       Example 1: Generate values from the uniform distribution on the
       interval (a, b).
          r = a + (b-a).*rand(100,1);
 
       Example 2: Use the RANDI function, instead of RAND, to generate
       integer values from the uniform distribution on the set 1:100.
          r = randi(100,1,5);
 
       Example 3: Reset the random number generator used by RAND, RANDI, and
       RANDN to its default startup settings, so that RAND produces the same
       random numbers as if you restarted MATLAB.
          rng('default')
          rand(1,5)
 
       Example 4: Save the settings for the random number generator used by
       RAND, RANDI, and RANDN, generate 5 values from RAND, restore the
       settings, and repeat those values.
          s = rng
          u1 = rand(1,5)
          rng(s);
          u2 = rand(1,5) % contains exactly the same values as u1
 
       Example 5: Reinitialize the random number generator used by RAND,
       RANDI, and RANDN with a seed based on the current time.  RAND will
       return different values each time you do this.  NOTE: It is usually
       not necessary to do this more than once per MATLAB session.
          rng('shuffle');
          rand(1,5)
 
    See Replace Discouraged Syntaxes of rand and randn to use RNG to replace
    RAND with the 'seed', 'state', or 'twister' inputs.
 
    See also RANDI, RANDN, RNG, RANDSTREAM, RANDSTREAM/RAND,
             SPRAND, SPRANDN, RANDPERM.

    Documentation for rand
       doc rand

    Other uses of rand

       codistributed/rand        distributed/rand    qrandstream/rand
       codistributor1d/rand      gpuArray/rand       RandStream/rand
       codistributor2dbc/rand    matlab/rand

READ THE DOCUMENTATION WHEN YOU DON'T UNDERSTAND SOEMTHING.

And then TRY IT OUT! For example:

rand(1,1)

ans = 0.6804

Along the way, you would learn about what rand returns, a stream of uniformly distributed random numbers. How many such numbers does the call rand(1,1) produce? (Exactly 1 of them.)

But where do they live? What does a uniformly distributed random number mean? What interval does the distribution lie in? If you don't know, then go back up and read the help again. Hint: It talks about the open interval (0,1).

Now, what happens when you mutlply such a number that originally lives in the interval (0,1), by some constant? Now where does that product live? In this case, you multiplied by the constant (0.19 - 0.17), which is just 0.02. It would seem logical that the product lies in the still open interval (0,0.02).

Similarly, now add some constant to that number. Where does it live?

As I said, you take apart the expression that you don't understand, startgin at the inside, then working out, going by the order of operations. So we would have this sequence of operations we need to understand.

rand(1,1)

rand(1,1)*(0.19 - 0.17)

0.17 + rand(1,1)*(0.19 - 0.17)

Each of them changes the previous result in a specific way. But we should be able to understand what the final result does, from each of those steps. Finally, perhaps a histogram might help.

X = 0.17 + rand(1,1000000)*(0.19 - 0.17);
histogram(X,'norm','pdf')

Of course now you might ask what this last line of code does as written. And again, you learn that by simply reading the help.