Variable declaration in matlab

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Shalini
Shalini 2012-3-5
评论： Walter Roberson 2017-6-25
Is it necessary to declare a variable in matlab?

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Walter Roberson
Walter Roberson 2012-3-5
There are some conditions under which it is necessary to initialize a variable ahead of time. These conditions have to do with "closures" and nested functions, and "poofing" variables.
Also, variables that will be used for with the code generator take their generated data type from the first assignment to the variable within the code.
Variables that are marked "global" must be declared as global before they are used; likewise with "persistent" variables.
There are no declarations such as in C or PASCAL, but there is enough leakage from the original "no declarations" model that the answer is more "not usually" than "no".
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James Tursa
James Tursa 2012-12-20
Sideways Comment: You can declare an unitialized numeric, char, or logical variable with a mex routine using unofficial API functions. E.g., see the UNINIT function from this FEX submission:
http://www.mathworks.com/matlabcentral/fileexchange/31362-uninit-create-an-uninitialized-variable-like-zeros-but-faster
Also, to clarify Jan's comment, when an unitialized cell or struct element is referenced (i.e., one with a NULL pointer behind the scenes), MATLAB will create a temporary empty 0x0 double matrix on the fly.

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Aldin
Aldin 2012-3-5
Yes, when in you type in command window:
a = 2; it's a number (in JAVA: integer)
a = '2'; it's a string (in JAVA String)
a = [1 2 3 4 5] it's a vector(array) (in JAVA: int array[] = new int[5])
a = [ 1 2; 3 4] it's a matrix (in JAVA: int array[][] = new int[2][2])
a = {'a',2;'b',3} it's a cell (in JAVA structure)
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Aldin
Aldin 2012-3-5
MATLAB works with only with matrix variable!!!
Oleg Komarov
Oleg Komarov 2012-3-5
What is a matrix variable?

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Shalini
Shalini 2012-3-5
Can you give an example of declaration (integer/real) in a simple code?
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Walter Roberson
Walter Roberson 2012-12-20
In older versions of MATLAB, int32(12) worked by having 12 evaluated in double precision first, creating a temporary (nameless) double precision variable. That temporary variable was then passed to the int32() routine, which did the conversion, creating a second temporary variable but of int32 type. That second temporary variable was returned from int32, after which the first temporary variable was deleted. The second temporary variable was then assigned to "second", which would happen by creating a permanent name for the nameless variable (not by copying its content, just naming it and holding on to it.)
In newer versions of MATLAB, int32() and similar numeric datatypes applied to constant numeric expressions of a very limited number of forms (e.g., uint64(134324342332432)) is handled at parsing time, special processing to ensure that the full precision is used; the parsing would directly create a temporary int32 variable. The assignment of that temporary variable to "second" would proceed like above, by assigning a permanent name to it rather than by copying it.
However, some testing I did a few weeks ago showed that if the numeric constant was not in one of a very limited number of formats, then even though it was numeric and constant, the special case would not be recognized, and instead the same sort of processing would be applied as for older MATLAB.
Mohashin Pathan
Mohashin Pathan 2013-5-27
i want to initialize some double and some integer in a structure, can anyone help me how to do that

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KJDS SRINIVASA RAO
KJDS SRINIVASA RAO 2013-5-27
yes sometimes required to remove confusion
Jon Camilleri
Jon Camilleri 2015-11-15
So how do I initialize a variable and read the data types available?
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Stephen23
Stephen23 2017-6-25
@ARUN BORGOHAIN: please ask a new question. Note that your question has nothing to do with declaring variables: you need to ask about how to use fminsearch properly.
Walter Roberson
Walter Roberson 2017-6-25
fun0 = inline('((x-5)^2+(y-5)^2-25)')
fun = inline('fun0(xy(1),xy(2))');
a = fminsearch(fun, [0 0])

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