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How does the MATLAB symvar function work?


By : Ahmed Maher
Date : October 17 2020, 06:10 PM
With these it helps I'm guessing you typed help symvar into the MATLAB Command Window, which is normally the best first step, but in this case you may have come across a small pitfall. This is because symvar is an overloaded function: there is more than one copy, and the copy that gets called depends on the data type/class of the variables/objects that are passed to it. You can see all the versions by using the which function with the -all option. The output I get on R2018a is:
code :
>> which symvar -all
C:\Program Files\MATLAB\R2018a\toolbox\matlab\funfun\symvar.m
C:\Program Files\MATLAB\R2018a\toolbox\curvefit\curvefit\@fittype\symvar.m  % fittype method
C:\Program Files\MATLAB\R2018a\toolbox\symbolic\symbolic\@sym\symvar.m      % sym method
C:\Program Files\MATLAB\R2018a\toolbox\matlab\funfun\@inline\symvar.m       % inline method
 symvar Finds the symbolic variables in a symbolic expression or matrix.
     symvar(S), where S is a scalar or matrix sym, returns a vector sym
     containing all of the symbolic variables appearing in S. The
     variables are returned in lexicographical order. If no symbolic variables
     are found, symvar returns the empty vector.
     The constants pi, i and j are not considered variables.

     symvar(S,N) returns the N symbolic variables closest to 'x' or 'X'.
     If N exceeds the number of variables appearing in S, or equals inf,
     then all variables appearing in S are returned.
     Upper-case variables are returned ahead of lower-case variables.
     If S is a symbolic function the inputs to S are listed in front of the
     other free variables. 

     Examples:
        syms alpha a b x1 y

        symvar(alpha+a+b) returns
         [a, alpha, b]

        symvar(cos(alpha)*b*x1 + 14*y,2) returns
         [x1, y]

        symvar(y*(4+3*i) + 6*j) returns
         y


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function does not work in Matlab


By : Dnyce Oak
Date : March 29 2020, 07:55 AM
it should still fix some issue I am surprised why following code does not work , try replace
code :
q = randn(500,1);
q = randn( size( t ) );
q = rand( size( t ) );   

Converting MATLAB 'imagesc' function to work with R's 'imagesc' from R's 'matlab' library


By : John Johnson
Date : March 29 2020, 07:55 AM
wish of those help I reckon you can get the same effect as clims by pre-processing your data so that values outside the range are squeezed to the range limits.
code :
z = matrix(rnorm(10*10, sd=3), 10)

z2 <- z
z2[z2 > 3] <- 3
z2[z2 < -5] <- -5

# or simply
z2 = scales::squish(z, c(-5, 3))

filled.contour(z)
filled.contour(z2)

Declare variables returned with symvar (MATLAB)


By : user2683651
Date : March 29 2020, 07:55 AM
hop of those help? I'm trying to declare a function (n-dimensional) and its variables from an input, regardless of how many variables I have in this function. Example: , How about:
code :
>> vars = symvar('3*x*y^2 + x^3 -3*x');
>> syms(vars{:})
>> whos x y
  Name      Size            Bytes  Class    Attributes

  x         1x1               112  sym                
  y         1x1               112  sym                

How does dist function work in MATLAB?


By : offandennui
Date : March 29 2020, 07:55 AM
wish of those help I have a MATLAB code which I try to convert to C, and it works all fine, but I'm stuck at dist function. It says that it calculates the Euclidean distance weight function. Calculating the normal Euclidean distance function is pretty easy, but I don't exactly get what the weight means here. In the code that I want to convert there is 1x1000, or to say in another words just a row array with complex values (meaning x + yi). Then it does something like this: , Here the
code :
((dist(sest(i), -1)) 
abs(sest(i) + 1)
abs(1-sest(i))
((dist(sest(i), -1)) 
conj(abs(real(sest(i)) + 1)+ imag(sest(i))*j)
((dist(sest(i), 1))
abs(1 -real(sest(i))) + imag(sest(i)*j)

Python alternative of the Matlab symvar function


By : Elisa Alvarez
Date : March 29 2020, 07:55 AM
will be helpful for those in need One way to get the list of identifiers from a Python expression is to use the ast module:
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