Loren on the Art of MATLAB

Turn ideas into MATLAB


Loren on the Art of MATLAB has been retired and will not be updated.

Thoughts about Anonymous Functions

One of the reasons I like using anonymous functions is because they allow me to express whatever function I want to use as a function of the relevant arguments in different contexts.



Here's a very general way I can write the code meant to generate points on a straight line.

straightline = @(X,slope,intercept) slope*X + intercept
straightline = 

Choose a Particular Line to Plot

First let's choose a particular straight line segment. I start by defining the slope and intercept values.

m = 2;  % slope
b = -3; % intercept

Plot the Line

Now I can evaluate my function when I create the plot.

x = 2:0.1:5;

Find Area Under the Line

Now let's find the area under a segment of this line, between two points. Since the function integral requires the integrand to be a function of one variable only, we can use the anonymous function myline, defined below, to create just such a representation.

lowerlimit = 2;
upperlimit = 5;

Create a function representing my particular line segment, by fixing those slope and intercept values, and creating a new function from the original one.

myline = @(x) straightline(x,m,b);

Use this new function, myline, as the integrand.

myarea = integral(myline, lowerlimit, upperlimit)
myarea =

Find Best Fit Line

Now suppose we have data, based on this line segment, that has some noise. And we would like to estimate the slope and intercept values.

m = 2;
b = -2;
t = (2:0.2:5)';
data = straightline(t,m,b) + 0.2*randn(size(t));

Now I want slope and intercept to be my independent variables. I can use polyfit. Of course, I could use \ as well.

p = polyfit(t,data,1);

Now compare estimates for slope and intercept to original values.

comparison = [m, b; p]
comparison =
            2           -2
        2.094      -2.3638

Perhaps I instead want a function of the slope and intercept only. In that case, with data supplied, I can derive such a function from straightline. I can even get the values put into a

slopeIntercept = @(slope,intercept) straightline(data, slope, intercept);
slp = [1 4]; intcpt = [0 -5];
newline1 = @(X) straightline(X, slp(1), intcpt(1));
newline2 = @(X) straightline(X, slp(2), intcpt(2));

Anonymous Functions Allow Interface Flexibility

Using the same original function definition for straightline, I am able to mold the function for different purposes. In the first case, I turned my function of 3 variables into a function of one variable, with preset parameters. I could also use it to create a function of just slope and intercept, suitable for create line segments for different parameters at a later time.

In fact, if I was trying to use my straightline function with some other code that required lines to be defined by slope and intercept first, and then the abscissa, I can easily create a new interface for the line.

differentLine = @(slope, intercept, X) straightline(X, slope, intercept);

Have You Used Anonymous Functions to Alter the Interface?

I'd love to hear your thoughts here.

Published with MATLAB® 7.14

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