Wouldn’t it be nice to have units to go with those numbers you compute in MATLAB?
% Velocity in kilometers per hour v = 12.3 * u.kph % Time in seconds t = 3.7 * u.second % Distance travelled d = v * t % Convert distance to feet u2num(d, u.foot) % Another method to convert distance to feet d/u.ft
v = 3.4167 m - s t = 3.7000 s d = 12.6417 m ans = 41.4753 ans = 41.4753
I’ve always wanted this functionality in both MATLAB and Simulink. When I was a student in University, MATLAB was my favorite programming tool, but I didn’t use it much for engineering homework, as there were other tools that had nice worksheets and included units with unit conversions and computations.
Even as an employee of MathWorks I’ve found myself using other math software to assist with computations that required careful tracking and conversion of units.
The two key elements for me are it is:
- Easy to use
- Well documented
The inclusion of units by just simply multiplying by the desired unit is a well thought out mechanism. Also, there are of course functions and methods to extract values of a specific unit type.
And there is unit consistency checking, making sure that you don’t attempt to do things like convert a distance to a temperature.
try u2num(d, u.kelvin) catch Me disp(Me.message); end
Incompatible input dimensions
The attention to detail and planning the functionality provides for easy use of this tool. For example, Sky included functions for unit conversion for standard MATLAB variables, not just the unit class. This means you don’t have to think about whether or not a particular variable is of the DimVar class or not.
a = pi; u2num(a)
ans = 3.1416
The organization and documentation of the code makes it pretty easy to add additional functions that enable conversions. For example, many times I may want to include the result of a particular computation as a variable in Simulink. With the addition of units in Simulink (R2016a) there can be consistency between the environments.
g = 9.81 *u.m/u.s^2 % Create Simulink.Parameter object with the same value and units as "g" gParam = u2param(g)
g = 9.8100 m --- s^2 gParam = Parameter with properties: Value: 9.8100 CoderInfo: [1×1 Simulink.CoderInfo] Description: '' DataType: 'auto' Min:  Max:  Unit: 'm/s^2' Complexity: 'real' Dimensions: [1 1]
Now the units engine in Simulink will be able to help with things like units consistency checking when this variable “gParam” is used in the Simulink model.
type u2param type getUnitString
function p = u2param(v) assert(isa(v, 'DimVar')); s = getUnitString(v); p = Simulink.Parameter(u2num(v)); p.Unit = s; end function s = getUnitString(v) assert(isa(v, 'DimVar')); [num, dem] = display(v); s = sprintf('%s/%s', num, dem); end
Getting the units of a value as a string that can be interpreted by other MATLAB and Simulink tools would be helpful.
Technically the UNITSOF function returns the unit string of an object, but in a specialized format.
This can be remedied pretty easily with the following:
[numerator, denominator] = display(g); [numerator '/' denominator]
ans = 'm/s^2'
And of course as or R2017a, you can do things like:
numerator + "/" + denominator
ans = "m/s^2"
There are some addons that do support physical units.
Simulink now has a notion of units on signal lines.
The Simscape products all require the use of specific units when defining properties of physical elements.
Let us know here.
Published with MATLAB® R2017a
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