Anyone use Matlab?

Smokey 6 litre · 11 Dec 2006, 15:14 (Ref:1788060)

I'm not expecting a huge responce from this thread but i was wondering if anyone out there is familiar with the use of the MatLab software?
I need to use it for some coursework and i'm particuarly stuck on ONE question! So please if anyone is an ace at this could you help me, please...

Tony_Simpson · 11 Dec 2006, 18:47 (Ref:1788214)

i do use MATLAB, but only small parts of it.

what seems to be the problem??

avsfan733 · 12 Dec 2006, 05:51 (Ref:1788635)

shot my man...i would honestly try the help menu though it is quite simply amazing

ubrben · 12 Dec 2006, 07:42 (Ref:1788681)

Go ahead, I'm a fairly heavy Matlab user.

BTW, have you tried the forums at matlabcentral.com?

Ben

imull · 12 Dec 2006, 20:08 (Ref:1789224)

just came out in a cold sweat and started shaking. god I hated using that program at uni

cracking bit of kit though!

Matlab central and the help menu as the others have said. both brilliant resourses...

The STIG · 12 Dec 2006, 21:31 (Ref:1789304)

Do not mention Matlab in my presense, got to use it for Uni Coursework and I don't like it at all!

Because I can't get the dammed thing to work, that's why!

ubrben · 12 Dec 2006, 21:45 (Ref:1789318)

Quote:

Originally Posted by The STIG

Do not mention Matlab in my presense, got to use it for Uni Coursework and I don't like it at all!

Because I can't get the dammed thing to work, that's why!

It's incredibly powerful and much easier than programming languages like C++.

What won't it do?

Ben

The STIG · 12 Dec 2006, 21:47 (Ref:1789320)

Quote:

Originally Posted by ubrben

It's incredibly powerful and much easier than programming languages like C++.

What won't it do?

Ben

uh... anything I want it too!

Tony_Simpson · 12 Dec 2006, 23:58 (Ref:1789402)

Quote:

Originally Posted by The STIG

uh... anything I want it too!

Your telling it the wrong things then!!!!

SteveT · 13 Dec 2006, 04:11 (Ref:1789522)

Well what's your question. Matlab is an excellent programming environment.

ubrben · 13 Dec 2006, 08:37 (Ref:1789624)

Quote:

Originally Posted by The STIG

uh... anything I want it too!

What do you want it to do, and what did you try?

The "getting started" help is very good, so if you can't get it to do anything I'd be surprised and/or worried.

Ben

Smokey 6 litre · 13 Dec 2006, 13:10 (Ref:1789832)

I'm quite supprised, i didn't know that the programe was widely used, thats why in my original post i said i didn't expect many replies.

I have 1 question to do for a piece of coursework, i've done all the rest but this is the sticking point.

7. Plot the two graphs y=3e-x and y=2sinx on the same plot. Use different colours and line-styles. Choose your own scales on the axes. Add a title to the graph and annotate to indicate which graph is which.

i got to this...

>> plot(((3*(2.71828183^-x))'c--'), [-6,2])
>> hold on
>> plot((2*sin*x,'r-'), [-6,2])
>> xlabel('x-axis')
>> ylabel('y-axis')
>> title(['Plot of y=3*e^-x and y=2*sin*x'])
>> text(150,19,'\it{y=3*e^-x}')
>> text(150,21,'\it{y=2*sin*x}')

and am now truly stuck as matlab wont accept it (it will accept parts of it). I am doubtful that anyone who doesn't use matlab regularly could help but if you could i'll be very grateful.

rcarr · 13 Dec 2006, 14:30 (Ref:1789898)

My friend who works for a DTM/FIA GT team swears by Matlab.
It is used in industry.

Smokey 6 litre · 13 Dec 2006, 14:43 (Ref:1789904)

Good to know that i am not strugling with it for nothing then.

ubrben · 13 Dec 2006, 15:11 (Ref:1789914)

Quote:

Originally Posted by Smokey 6 litre

I'm quite supprised, i didn't know that the programe was widely used, thats why in my original post i said i didn't expect many replies.

I have 1 question to do for a piece of coursework, i've done all the rest but this is the sticking point.

7. Plot the two graphs y=3e-x and y=2sinx on the same plot. Use different colours and line-styles. Choose your own scales on the axes. Add a title to the graph and annotate to indicate which graph is which.

i got to this...

>> plot(((3*(2.71828183^-x))'c--'), [-6,2])
>> hold on
>> plot((2*sin*x,'r-'), [-6,2])
>> xlabel('x-axis')
>> ylabel('y-axis')
>> title(['Plot of y=3*e^-x and y=2*sin*x'])
>> text(150,19,'\it{y=3*e^-x}')
>> text(150,21,'\it{y=2*sin*x}')

and am now truly stuck as matlab wont accept it (it will accept parts of it). I am doubtful that anyone who doesn't use matlab regularly could help but if you could i'll be very grateful.

You clearly haven't read the slightest thing about how Matlab works. Open Matlab and press F1 and go to "Getting Started with Matlab" in the help and read it.

Despite the fact that you have a homework assignment you haven't prepared for, I'll help you because Matlab is one of the most useful things you can learn if you want to work in Aerospace or Motorsport. PI V6 exports data directly in Matlab .MAT format - it does this for a reason.

Right, now what have you done wrong?

You haven't defined x. Matlab isn't normally symbolic (it has a symbolic tool box but you don't need it for what you're doing)

To calculate the two equations you need:

x = [0:0.1:10]

This creates an array of x numbers you can operate on from 0 to 10 in 0.1 increments. You didn't specify the range you needed, adjust accordingly and search the help for defining arrays.

Then you need;

y = 3.*(exp(-x));

and

y2 = 2.*(sin(x));

The . before the * sign means you are doing array multiplication not a matrix calc. You multiplying by one number so it doesn't matter, but it's good to understand the difference. Read the help.

The semi-colon supresses the output so you don't fill the command window with numbers.

Ok you now want to plot your two functions:

plot(x,y,x,y2)

You then need to lable the graph:

legend('y = 3e^-^x','y = 2sinx' )

The ^ make the following character superscript. Type help legend in the command prompt for help.

You then need a title and x and y labels. I'll let you find the help for those.

Ben

William Dale Jr · 13 Dec 2006, 15:14 (Ref:1789916)

I did a subject on using Matlab in first year, but that was a while ago now. It still pops up every now and then, and it's probably come up more and more in the next couple of years of my degree.

I hate it because I don't know how to use it properly, but I'm getting better

Anyway, a couple of things come to mind:

In my experience, to plot something like that, you need to give matlab an array of values for x to equal. Is that what the -6 and 2 are there for? If so, you need to set it up independently before you put it into the plot function, like so:

x = [-6:0.1:2]

The number between the semi-colons defines the size of the steps (i.e. it'll generate a one-row matrix with the values [-6, -5.9, -5.8, ... , 1.9, 2] )
For the sake of clarity, define your y-equations (using variable names like y1 and y2) and then plug those variables into the plot function, so your plot function just looks like:
plot(x,y1)
or plot(x,y2)
or plot(x,y1,x,y2) if you want to be tricky and plot them both using the same function instead of using 'hold on'.
Have a look under plot in the help section of the program to show you how to label stuff and change axis names; it'll tell you more than I ever could!

Hope I've pointed you in the right direction, but there's every chance that I haven't. F****** Matlab!

EDIT: Just follow Ben's explanation. It's better than mine!

Smokey 6 litre · 13 Dec 2006, 17:14 (Ref:1789967)

Right i have now sucessful completed by Matlab assignment and a big thank you to everyone who has posted coments here, and especially BIG THANKS go out to Ubrben and William Dale Jr.

Well done boys, now that i've done it its obvious where i was going wrong, stupid stuff really.

THANK YOU

avsfan733 · 14 Dec 2006, 06:20 (Ref:1790300)

From personal experience...I don't bother coding in x and y labels...I have found it much easier to use the axis edit tool which will save the data you put in.

as ubrben said...the help menu is like mecca. There is very little matlab can't do. I utilized it last semester to basically hand code a finite difference program for a heat transfer project. if you have questions find the help and read it. it almost always has examples which are usually very helpful.

ubrben · 14 Dec 2006, 07:43 (Ref:1790346)

Quote:

Originally Posted by avsfan733

From personal experience...I don't bother coding in x and y labels...I have found it much easier to use the axis edit tool which will save the data you put in.

as ubrben said...the help menu is like mecca. There is very little matlab can't do. I utilized it last semester to basically hand code a finite difference program for a heat transfer project. if you have questions find the help and read it. it almost always has examples which are usually very helpful.

I don't tend to hard code labels either... unless I'm processing a large number of input files of test data that have naming conventions that tell me something about the test condition. In this case you can loop plot generation and automatically create all the plots as you want.

Ben