Engineering Thread

devinejay · 19-02-2009 12:36AM

Also have a program that churns out roman numerals like nobody's business. The only problem is it is quite cumbersome. I'm using four "switch" functions when I could probably have one in a function and call it four times. I guess I'll just do the usual and spend the free time before the actual lab in the mac lab, programming away, then regurgitate the program once again when the instructors arrive in, much to the bewilderment of my partner who possibly doesn't realize how long I've already spent on it. The joys of computer science.

Jonathan · 19-02-2009 01:04AM

devinejay wrote: »

Also have a program that churns out roman numerals like nobody's business. The only problem is it is quite cumbersome. I'm using four "switch" functions when I could probably have one in a function and call it four times. I guess I'll just do the usual and spend the free time before the actual lab in the mac lab, programming away, then regurgitate the program once again when the instructors arrive in, much to the bewilderment of my partner who possibly doesn't realize how long I've already spent on it. The joys of computer science.

One function could do it all if you pass it the appropriate roman letters.

devinejay · 19-02-2009 01:10AM

jmccrohan wrote: »

One function could do it all if you pass it the appropriate roman letters.

well at the moment I have one function that returns roman numerals for a single digit, then I have four if statements checking whether it's dealing with tens, hundreds etc. which passes the appropriate numerals to the function which does it's thing, then at the end it adds it all together. Kinda what you mean?

devinejay · 19-02-2009 11:35AM

Wankel engines in 1E8, don't get over excited Baza!

mathew · 19-02-2009 12:05PM

who do you have for 1e8 now?

devinejay · 19-02-2009 01:45PM

Professor David Taylor, it seems mechanical engineering is about as interesting to some people in the class as Anil Kokaram's stuff was for me.

1E8, interesting?!!?:o

Brian · 19-02-2009 07:00PM

The one time I miss 1E8, and he did rotaries.. bleh, I bet I knew it all already.
dj-ygpm.

TheAmateur · 22-02-2009 06:14PM

Anyone got any idea how to integrate:

∫4udu/-(u^4)-(2u^3)+(2u)+1

?
I've been staring at it blankly for about two hours I think... got rid of the u up top to make
∫du/-(u^3)-(2u^2)+2+(u^-1)
but don't see how that can help. It looks like there could be (or should be) some partial fraction thing I can do, but if there is I can't see it... and I've checked everything up to that point again and again and I keep getting left with the same integration...:(

mathew · 22-02-2009 06:34PM

you sure you have the sum right??? answer is massive....

TheAmateur · 22-02-2009 06:46PM

It could be wrong. I might as well start from the start and explain where I got ∫4udu/-(u^4)-(2u^3)+(2u)+1 from.
The question is
∫dθ/cosθ+cotθ
so I used u = tan (θ/2) and got
∫(2du/1+(u^2))/(1-(u^2)/1+(u^2))+(1-(u^2)/2u)

simplified and got
∫2du/((2u-2(u^3)+1-(u^4))/2u)

simplified again and got
∫4udu/-(u^4)-(2u^3)+(2u)+1

How did you find out the answer is massive? I plugged it into Wolfram and got
-4*(-1/(4*(1 + x)^2) + 1/(4*(1 + x)) + Log[-1 + x]/8 - Log[1 + x]/8)
That what you mean by massive?

mathew · 22-02-2009 07:46PM

'fraid I dont have a clue... cant get anywhere with it.. tried trig functions and everything..
Its prob something easy enought too.. always is

big answer I got was from an online calculator.. attached..

TheAmateur · 22-02-2009 07:57PM

mathew wrote: »

'fraid I dont have a clue... cant get anywhere with it.. tried trig functions and everything..
Its prob something easy enought too.. always is

big answer I got was from an online calculator.. attached..

Hmmm. Just figured out (u^4)+2(u^3)-2u-1 is (u-1)((u+1)^3). Any use? Maybe I can use partial fractions now? I've nearly given up though. I mean, it's only worth one mark!!!

Peleus · 22-02-2009 08:00PM

TheAmateur wrote: »

It could be wrong. I might as well start from the start and explain where I got ∫4udu/-(u^4)-(2u^3)+(2u)+1 from.
The question is
∫dθ/cosθ+cotθ
so I used u = tan (θ/2) and got
∫(2du/1+(u^2))/(1-(u^2)/1+(u^2))+(1-(u^2)/2u)

simplified and got
∫2du/((2u-2(u^3)+1-(u^4))/2u)

simplified again and got
∫4udu/-(u^4)-(2u^3)+(2u)+1

How did you find out the answer is massive? I plugged it into Wolfram and got
-4*(-1/(4*(1 + x)^2) + 1/(4*(1 + x)) + Log[-1 + x]/8 - Log[1 + x]/8)
That what you mean by massive?

type that into wiley, if its the right answer you'll get it right no matter how undersimplified it is.

mathew · 22-02-2009 08:03PM

partial fractions with repeated roots arent the same as normal.. requires differentiation.. its very easy.. but not obvious..
very well explained here: http://www.swarthmore.edu/NatSci/echeeve1/Ref/LPSA/PartialFraction/PartialFraction.html

Might help..

TheAmateur · 22-02-2009 08:43PM

Peleus wrote: »

type that into wiley, if its the right answer you'll get it right no matter how undersimplified it is.

Heh it's not wiley it's no. 4 of those extra questions he gave us! Remember?

matthew wrote:

partial fractions with repeated roots arent the same as normal.. requires differentiation.. its very easy.. but not obvious..
very well explained here: http://www.swarthmore.edu/NatSci/ech...lFraction.html
Might help..

You should see the partial fraction equation now... it's like a monster! If I'm feeling super sadistic I might try work it out... it seems a shame to give up again after the breakthrough...

Brian · 22-02-2009 10:08PM

Mathew, would you mind explaining the logic of this "cover-up" thing? I can't get my mind beyond the apparent division by zero..

TheAmateur · 22-02-2009 10:12PM

Baza210 wrote: »

Mathew, would you mind explaining the logic of this "cover-up" thing? I can't get my mind beyond the apparent division by zero..

You trying the question too? I've officially given up. I haven't tried one or three, but I think I got two. It's for tuesday isn't it?

Brian · 22-02-2009 10:16PM

Not trying them no, I suck at Maths. I'm just trying to understand the notes that Mathew linked to.

I think the assignment's meant to determine who's been doing their integration using online integrators..

>_>

<_<

TheAmateur · 22-02-2009 10:28PM

Baza210 wrote: »

Not trying them no, I suck at Maths. I'm just trying to understand the notes that Mathew linked to.

I think the assignment's meant to determine who's been doing their integration using online integrators..

>_>

<_<

Online Integrators.... that's genius! Why didn't I think of that!!! All those hours...

mathew · 22-02-2009 10:35PM

Baza210 wrote: »

Mathew, would you mind explaining the logic of this "cover-up" thing? I can't get my mind beyond the apparent division by zero..

I'll do my best.. hard to do on here...

say we have A/(s+1) and B/(s+2)

The 'logic' is kinda weird..
To work out A, you find an s that will make the term under A 0, in our case thats -1.

No go back to the original one you're trying to expand. Ignoring, or 'covering up' the term that is the same as the term under A, put in your value for s.

That will give you the value of A.

Now do the same for B.

In the case where you have something like A/(s^2 + 1). In order for that term under A to be 0, the s^2 term has to be -1, therefore s = j ... ie the square root of -1.. It'll still work out..

Very handy method, until you get to repeated roots when things get a bit more complicated..

24-02-2009 07:32PM

ahhh 1st year. wiley plus.....piece-O-cake

wait until 2nd year guys:( things get a lot harder

i can only imagine what 3rd and 4th year are like

Jonathan · 24-02-2009 07:47PM

Trying to work out who you are Natalia Dirty Acid

mathew · 24-02-2009 10:25PM

oh.. @Baza or Amature...
could one of you post or pm me the solution to that integral problem when you get it.. its annoying me

godtabh · 24-02-2009 10:51PM

[quote=[Deleted User];59169458]ahhh 1st year. wiley plus.....piece-O-cake

wait until 2nd year guys:( things get a lot harder

i can only imagine what 3rd and 4th year are like

[/QUOTE]

Dont be telling lies

Brian · 24-02-2009 11:23PM

My C++ has

for

while

for

if

else

=/

TheAmateur · 24-02-2009 11:39PM

Does
it
work?

I've got
for
if
if
for
if
for
if
else
for

matthew wrote:

oh.. @Baza or Amature...
could one of you post or pm me the solution to that integral problem when you get it.. its annoying me

No problem... that is, if they ever give us the solution! Experiences so far have taught me not to expect any follow-up on assignments etc. given in. We're lucky if we even get them back, never mind marks and/or corrections. Still wondering if we'll ever get those reports we did for 1e8 back... I spent some time on that feckin thing.... Was it/is it always like this?

desertstorm · 25-02-2009 12:28AM

[quote=[Deleted User];59169458]ahhh 1st year. wiley plus.....piece-O-cake

wait until 2nd year guys:( things get a lot harder

i can only imagine what 3rd and 4th year are like

[/quote]

actually apparently it gets easier, I have a friend in 4th year civil and she says she hasnt got any maths lectures, but its a ton of project work

Brian · 25-02-2009 01:51AM

Frick. My array seems to have residual values, or whatever the heck they'd be called. There's values in the slots even though I haven't entered them. That means that I have to for-loop a negative value into every single slot before starting to input the array with a negative number sentinel..

The 4 bars on the right shouldn't be there at all.

What I get after the negative slot loading. Notice that the setw() bar still extends the same width

mathew · 25-02-2009 08:21AM

TheAmateur wrote: »

Does
it
work?

I've got
for
if
if
for
if
for
if
else
for

No problem... that is, if they ever give us the solution! Experiences so far have taught me not to expect any follow-up on assignments etc. given in. We're lucky if we even get them back, never mind marks and/or corrections. Still wondering if we'll ever get those reports we did for 1e8 back... I spent some time on that feckin thing.... Was it/is it always like this?

You get the 1e8 back eventually.. They take their time tho.. Never got a mark for autocad tho..

Boston · 25-02-2009 11:03AM

TheAmateur wrote: »

No problem... that is, if they ever give us the solution! Experiences so far have taught me not to expect any follow-up on assignments etc. given in. We're lucky if we even get them back, never mind marks and/or corrections. Still wondering if we'll ever get those reports we did for 1e8 back... I spent some time on that feckin thing.... Was it/is it always like this?

They're not paid to do corrections hence they're slow about doing them.

Baza, you should always initialise your variables.

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