how to set a unit to variable?

I encounter the error after run this :

    30*unit::mm

[Devarshi Patel]

Check below link if you have version greater than or equal to R2017A

https://in.mathworks.com/help/matlab/learn_matlab/character-strings.html

[Walter Roberson]

Discussion of character strings is not very relevant to the question of whether MATLAB can handle units.

Answer 1

[Karan Gill]

Units are now in MATLAB if you have Symbolic Math Toolbox. Try:

>> u = symunit; 
>> x = 2*u.meter 
x = 
2*[m]

>> x = rewrite(x,u.ft) 
x = 
(2500/381)*[ft]

>> double(separateUnits(x)) 
ans = 
    6.5617

See the tutorial: https://www.mathworks.com/help/symbolic/units-of-measurement-tutorial.html

[Walter Roberson]

Note: the implementation of units has difficulty with quantity 0, which tends to make the most difference with temperature (e.g., 0C and 0F)

Answer 2

[the cyclist]

In general, MATLAB variables do not have units, and what you have written is not a valid MATLAB syntax (to my knowledge).

There is a contribution to the File Exchange that allows for assigning unit to variables: http://www.mathworks.com/matlabcentral/fileexchange/29621-units-conversion-toolbox/content/UnitConversion-rev2/html/defining.html.

[Karan Gill]

Units are now in MATLAB if you have Symbolic Math Toolbox. See the tutorial: https://www.mathworks.com/help/symbolic/units-of-measurement-tutorial.html

Posted a separate answer below so that OP can accept.

Answer 3

[Steven Lord]

That syntax is specifically for use in the MuPAD Notebook Interface (as stated by the note at the top of this documentation page) not in MATLAB.

[fred bnm]

ok,but how to use mupad.i want define a variable in mupad and use that in matlab workspace.

[Walter Roberson]

http://www.mathworks.com/help/symbolic/copy-variables-and-expressions-between-matlab-and-mupad.html

You should consider instead using (at the MATLAB level)

30 * sym('unit::mm')

[Walter Roberson]

30 * sym('unit::mm')

is no longer supported. These days you should use symunit . Or if you are despairate,

30 * feval(symengine, 'unit::mm')