Do I need symbolic math toolbox to graph a function such as f(x)=ln(x) or f(x, y)=y^2/x

I just bought matlab and while processing data works well I cannot find how to graph functions from R to R for instance. Is it the case that I need to buy symbolic math toolbox in order to be able to do these graphings?

Answer 1

[Stephen23]

There is no need for the symbolic toolbox for such simple functions. Try this:

>> X = 0:0.1:3;
>> Y = log(X);
>> plot(X,Y)

Or your second example:

>> [X,Y] = meshgrid(0:0.1:2,1:5);
>> Z = Y.^2./X;
>> surf(X,Y,Z)

[Emilia]

Thank you, it works!

The part I don't understand is the first row of both examples, how do I know what numbers to put after X (or [X,Y])

That is appearly what I was initially missing.

[Stephen23]

You pick those numbers to suit your needs: what range do you want to plot, and with how many points? The introductory tutorials describe how to make vectors of values:

http://www.mathworks.com/help/matlab/getting-started-with-matlab.html

And for more detailed info:

http://www.mathworks.com/help/matlab/ref/colon.html

http://blogs.mathworks.com/loren/2006/11/10/all-about-the-colon-operator/

Tip use your favorite internet search engine to search the MATLAB documentation. Half of the questions we answer here are solved by simply reading the documentation.

[Walter Roberson]

Additionally:

If you had an expression in symbolic form because you were using the Symbolic toolbox, then you would still need to select particular ranges to plot it over. The plot routines cannot plot symbolic expressions directly: they can only plot the results of substituting in particular values into symbolic expressions and by so doing getting a numeric result.

You may also wish to look at ezplot()

Answer 2

[John BG]

Hi Emilia

if it's about just plotting a function, there is a new function that does not require the symbolic Tool box called fplot

fplot(@(x) log10(x))

.

the same applies to fsurf, no need for the previous mesh declaration

   fsurf(@(x,y) sin(x)+cos(y),'lines','none')
.

'

the field lines=none is optional

mesh also has a new fmesh

if you find this answer useful would you please be so kind to mark my answer as Accepted Answer?

To any other reader, please if you find this answer of any help solving your question,

please click on the thumbs-up vote link,

thanks in advance

John BG

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