Tags:
1. Oct 29, 2008

### intel2

how can someone do the attach calculation in Matlab?

#### Attached Files:

• ###### Picture1.png
File size:
3.6 KB
Views:
181
2. Oct 29, 2008

### shoehorn

Read the documentation. The Matlab getting started guide is particularly good, and will teach you how to perform calculations like this and more.

3. Oct 29, 2008

### intel2

i went through it but i couldnt get to work.. this is what i did:

for i = 0 : 100
for j = 1 : 101

dme = (sum (sum ((i/j)^ 2)+log(sqrt(j))));
end
end

4. Oct 29, 2008

### intel2

for i = 0 : 100
for j = 1 : 101
x= (i/j)^2;
y = (j)^.5;
end
end

F = (sum (x)+log(y))

5. Oct 29, 2008

### shoehorn

There are a couple of important things to note.

Firstly, Mathcad is an infamously flaky piece of software. Use it only if you have absolutely no alternative.

Secondly, the answer you've got from Mathcad is incorrect. The actual result of the summation you've given is

$$\sum_{i=0}^{100} \sum_{j=1}^{101} \left[ \left(\frac{i}{j}\right)^2 + \log\sqrt{j} \right] \approx 571831.873$$

You can verify this using Mathematica, Maple, Matlab, or your own C/C++/Python code. Again let me stress: Mathcad is absolutely atrocious software. I've seen the source, and it's not pretty. Avoid it like the plague.

Thirdly, to evaluate the sum in Matlab you can do something like the following:

Code (Text):

% First declare and initialize a dummy variable
x = 0;

% Now perform the summation:
for i = 0:100
for j = 1:101
x = x + (i / j)^2 + log(sqrt(j));
end
end

This should leave you with the variable x holding the result. Note that this is neither a particularly efficient nor elegant way of computing such a sum.

6. Oct 30, 2008

### Emreth

Actually the mathcad result is correct. In matlab, log means ln, log10 means log.The answer shoehorn gives is for ln.
so the code is
% First declare and initialize a dummy variable
x = 0;

% Now perform the summation:
for i = 0:100
for j = 1:101
x = x + (i / j)^2 + log10(sqrt(j));
end
end

Last edited: Oct 30, 2008
7. Oct 30, 2008

### intel2

Thank you to shoehorn and to Emreth ..

8. Oct 30, 2008

### intel2

since we r in the topic; how can i plot the attach equation between [-4,4] with a 0.001 interval using matlab

#### Attached Files:

• ###### untitled.JPG
File size:
3.6 KB
Views:
128
9. Oct 30, 2008

### Emreth

read the help files, this is quite trivial.

for i=1:3000
x(i)=-4+i/1000;
y(i)=-x^2-4*x-2;
end
for i=3000:5000
x(i)=-4+i/1000;
y(i)=abs(x);
end
for i=5000:8000
x(i)=-4+i/1000;
y(i)=2-exp(sqrt(x-1));
end
plot(x,y);

Last edited: Oct 30, 2008
10. Oct 30, 2008

### intel2

Tip of the Hat to Emreth ..

the way u wrote x(i) ,, is smart... once again thanks