ENG1060 Computing

[xZero]

with lab7 q5 b) and c), we use the z values from the table given instead of the polyfit value right? if so I got 0.8102 for part c which doesn't seem right :S

Edit: ok im a retard... i used x-values in my simpson's rule instead of z

[JinXi]

with lab7 q5 b) and c), we use the z values from the table given instead of the polyfit value right? if so I got 0.8102 for part c which doesn't seem right :S

Edit: ok im a retard... i used x-values in my simpson's rule instead of z

what rule did u use for part c? I used 1 single appl trapezoid and 2 simpson 1/3.

Gonna try some other combinations and see which one's the most accurate..

And yeah I think we're supposed to use the z-values from the tables. Not so sure about this though-.-

Edit: the Combination above doesn't work

[xZero]

i used 1 trapezoid for 0 and 0.1, 3/8 for 0.1 to 0.7 and 1/3 for 0.7 to 1.2 and my result is within 0.05%

[sajib_mostofa]

Cheers for that man. If I don't ask the user for the number of segments after the rule, then where should I ask them? Also was the m-file for this Q lengthy?

Just ask for the value of n after the rule had been chosen.

Eg if rule == 1
          n = input('.......')
          I = comtrapz(func,a,b,n);
    elseif rule == 2
          n = input('....')
             if
                 *Nested Loop here in case the user enters an odd number of segments
             end
          I = compsimpson1_3(func,a,b,n);
    end
And my M-File was about 50 lines with quite detailed comments. Probably 3x lines of pure code.

To repeat the calculation for the whole thing, do you need to use a while loop before or after this piece of code ^^ ?

[JinXi]

Cheers for that man. If I don't ask the user for the number of segments after the rule, then where should I ask them? Also was the m-file for this Q lengthy?

Just ask for the value of n after the rule had been chosen.

Eg if rule == 1
          n = input('.......')
          I = comtrapz(func,a,b,n);
    elseif rule == 2
          n = input('....')
             if
                 *Nested Loop here in case the user enters an odd number of segments
             end
          I = compsimpson1_3(func,a,b,n);
    end
And my M-File was about 50 lines with quite detailed comments. Probably 3x lines of pure code.

To repeat the calculation for the whole thing, do you need to use a while loop before or after this piece of code ^^ ?

It has to cover the Whole piece of code so it starts before and ends after =)

[sajib_mostofa]

Thanks for all the help man. 

[sajib_mostofa]

Can anyone tell me what value of the integral they got for 5a and b?

[JinXi]

with lab7 q5 b) and c), we use the z values from the table given instead of the polyfit value right? if so I got 0.8102 for part c which doesn't seem right :S

Edit: ok im a retard... i used x-values in my simpson's rule instead of z

Actually read the question again and for b and c, it said "Write an M-file that evaluates the integral" and "Modify the M-file in part (a) to evaluate the integral"

[sajib_mostofa]

Can anyone help me with Q4a of lab7? I don't understand why my loop keeps on returning a value of n = 1

% function inputs
a = -2;
b = 4;
func = @(x) 1-x-4*x.^3+2*x.^5;

% Analysing analytically
I_1 = 1104;

n = 1;
I = comtrapz(func,a,b,n);
error = (I_1 - I)/I;
while error<0.01
    n = n+1;
end

[xZero]

while error<0.01
    n = n+1;

after adding a segment, you're suppose to recalculate the estimated integral and error within the while loop

Actually read the question again and for b and c, it said "Write an M-file that evaluates the integral" and "Modify the M-file in part (a) to evaluate the integral"

I just evaluated the integral using the datapoints given oO

[sajib_mostofa]

while error<0.01
    n = n+1;

after adding a segment, you're suppose to recalculate the estimated integral and error within the while loop

Actually read the question again and for b and c, it said "Write an M-file that evaluates the integral" and "Modify the M-file in part (a) to evaluate the integral"

I just evaluated the integral using the datapoints given oO

I tried but the loop isn't ending

[xZero]

type the code up if you're still having problem with it

[sajib_mostofa]

% function inputs
a = -2;
b = 4;
func = @(x) 1-x-4*x.^3+2*x.^5;

% Analysing analytically
I_1 = 1104;

n = 1;
I = comtrapz(func,a,b,n);     % Composite trapezoidal function
error = (I_1 - I)/I;
while error<0.01
    n = n+1;
    I = comtrapz(func,a,b,n);     
    error = (I_1 - I)/I; 
end

[JinXi]

% function inputs
a = -2;
b = 4;
func = @(x) 1-x-4*x.^3+2*x.^5;

% Analysing analytically
I_1 = 1104;

n = 1;
I = comtrapz(func,a,b,n);     % Composite trapezoidal function
error = (I_1 - I)/I;
while error<0.01
    n = n+1;
    I = comtrapz(func,a,b,n);      
    error = (I_1 - I)/I;  
end

lol you forgot an absolute sign. I_1 will always be smaller than I which results in a -ve number, which will always be smaller than 0.01 hence an infinite loop  

Just add the abs() for your error and it should work fine.

Edit: Your Inequality sign is also the wrong way around. If you did that abs already, the error will be larger than 0.01 at the 1st iteration and hence the loop stops, since what you're loop is doing is run WHIle the Error is < 0.01, when it should run when it's >0.01.

[sajib_mostofa]

Thanks for that man, working fine now