1. Electrical and Computer Engineering Department SUNY – New Paltz
Computer Simulation
“Lecture 8”
Electrical and Computer Engineering Department
SUNY – New Paltz
SUNY-New Paltz

2. Loops objectives code determinate loops with “for”
code indeterminate loops with
“while”
SUNY-New Paltz

3. Exercise
Write a MATLAB program that prompts the user for a number, n. Your program should use a “for” loop to calculate n!
SUNY-New Paltz

4. Determinate repetition with for
There are 4 balls: R, B, G and Y.
How many combinations of pairs of 2 balls are there?
(R,B), (R,G), (R,Y),
(B,G), (B,Y), (G,Y)
SUNY-New Paltz

5. Combination of r out of n
SUNY-New Paltz

6. Exercise
Write a short MATLAB program that uses 2 for loops, to calculate the combination formula in the previous slide.
SUNY-New Paltz

7. Exercise
Write a short MATLAB program that uses ONLY 1 for loop, to calculate the combination formula in the previous slide.
SUNY-New Paltz

8. MATLAB Code
SUNY-New Paltz

9. Nested for’s N=4; M=4; L=4; for i=1:N for j=1:M for k=1:L
a(:,:,1) =
a(:,:,2) =
a(:,:,3) =
a(:,:,4) =
N=4;
M=4;
L=4;
for i=1:N
for j=1:M
for k=1:L
a(i,j,k)=i+j+k;
end
SUNY-New Paltz

10. Exercise
1- Manually create vector ‘a’ and use imshow(a) to display the grey view of it:
2- Manually create matrix ‘b’ and display:
3- Manually create matrix ‘c’ to display a checkered board.
* Hint – use (‘InitialMagnification’, 1000 ) to magnify it!
SUNY-New Paltz

11. Exercise
1- Write a MATLAB program (using for loops) to create vector ‘a’ in last exercise.
2- Write a MATLAB program (using for loops) to create matrix ‘b’ in last exercise.
3- Write a MATLAB program (using for loops) to create matrix ‘c’ in last exercise.
SUNY-New Paltz

12. How can we terminate a for loop?
Use “break” inside the loop and it will terminate the loop!
for k = 1:100
disp(k)
if( k == 50)
break;
end
for k = 1:100
disp(k)
end
SUNY-New Paltz

13. Exercise
Prompt the user to enter a number. If the number is positive then print the square root of it and ask for another number. Otherwise, exit the loop. Hint: initially use a loop that iterates for 20 times.
SUNY-New Paltz

14. Indeterminate repetition with while
SUNY-New Paltz

15. Doubling time of an investment
We would like to know how long it takes for the investment to double:
1. Initialize balance, year, interest rate
2. Display headings
3. Repeat
Update balance according to interest rate
Display year, balance
until balance exceeds twice original balance
4. Stop
a = 1000;
r = 0.1;
bal = a;
year = 0;
disp( ’Year Balance’ )
while bal < 2 * a
bal = bal + r * bal;
year = year + 1;
disp( [year bal] )
End
Year Balance
SUNY-New Paltz

16. Exercise Repeat the previous exercise, but use a while loop.
SUNY-New Paltz

17. Exercise
Find the sum of the series s=1 +1/(2*2) + 1/(3*3) + … for a 1000 terms. Use a for loop.
Use a while loop to do the above and stop when a new term is less than .01
SUNY-New Paltz

18. Solution clc clear all format long mysum = 0; n = 1;
delta = ;
while 1/(n*n) > delta
mysum = mysum + 1/(n*n);
n = n +1;
end
disp(mysum)
SUNY-New Paltz

19. break and continue Break : exits the while loop
Continue : starts a new iteration
SUNY-New Paltz

20. exercise
In the previous example, write a while loop that runs for ever, i.e. while(1), then break the loop when the condition takes place.
SUNY-New Paltz

21. Exercise clc clear all format long mysum = 0; n = 1;
delta = ;
while 1
mysum = mysum + 1/(n*n);
if 1/(n*n) < delta
break
end
n = n +1;
disp(mysum)
SUNY-New Paltz

22. Menus
k = menu( ’Click on your option’, ’Do this’, ’Do that’, ’Quit’ );
k = 0;
while k ~= 3
k = menu( ’Click on your option’, ’Do this’, ...
’Do that’, ’Quit’ );
if k == 1
disp( ’Do this ... press any key to continue ...’ )
pause
elseif k == 2
disp( ’Do that ... press any key to continue ...’ )
end
SUNY-New Paltz

23. Exercise
Set up a menu that prompts the user to select a waveform from the following selections:
1- sin(x)
2- cos(x)
After the user makes a selection your program should show the graph ([0 – 2pi] in a new window.
SUNY-New Paltz