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Hi,
I have a laplace function:
<br />
30/(3+s)^2<br />
I am trying to find the inverse of it.
I know the answer from (MATLAB) is
<br />
30*exp(-3*t)*t<br />
Could anyone lend a hand on getting from A to B on this one?
I know that to get the answer above, the original equation must be re-arranged to be:
<br />
30/(s+3)*(1/s^2) <- this is wrong :-(.<br />
<br />
where:<br />
<br />
30/(s+3) transforms to 30*exp(-3*t)<br />
(1/s^2) transforms to t<br />
Any help would be appreciated.
Cheers,
modified on Sunday, May 4, 2008 3:11 AM
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Isn't this just the nth power with frequency shift transform?
i.e: 1/(s+a)^(n+1)
In this case, a=3 and n = 1
the transform is t^n/n! * exp(-at) so with a = 3 and n = 1:
t^1/1! * exp(-3t)
=texp(-3t)
Since 30 is a constant it doesn't affect the transform and we just put it back in:
30*t*exp(-3t)
This is just an application of the shifting theorem:
For an arbitrary constant a > 0
L{exp(-at)f(t)} = F(s+a)
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Yea it was the 1st shifting theorom. (like you said above).
Cheers,
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Meh, Freud would laugh at me..
I read "Need help inverting a LAPDANCE function"
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haha, math would be bigger than sport if that was the way of things 
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How can i make good s-box easily (against linear and differential attacks)? If i used prepaid one that may belongs to someone or standard ciphers then it would be plagiarism right? So i need to make own s-box (8 bit input, 8 bit output (16x16)). Please Please suggest me any way to decide it.
Thank you.
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Bimbaa wrote: How can i make good s-box easily (against linear and differential attacks)?
I think that's a rather non-trivial exercise.
Bimbaa wrote: If i used prepaid one that may belongs to someone or standard ciphers then it would be plagiarism right?
Plagiarism? In what sense? Is this a homework assignment? If so, then simply copying and pasting an s-box implementation would be plagiarism, yes. If it's for personal use, I don't think it would be plagiarism if referenced accordingly.
This[^] could be of use to you.
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WELL I HOPE ALL USERS ARE IN GOOD SPIRITS...FOR TOMORROW IS A FRIDAY AND RELIEF TO A WEEK.
I'M A FRIENDLY NEWBIE POWERUSER WITH AN OPEN MIND AND WEAK HEART.
I have a project for c++ and I need help for the first time. Source CODE IN C++
the word problem:
the department of motor vehicles administers a written driver's exam consisting of 20 multiple choice questions. an applicant for the drivers license exam answers these questions electronically and the answers are stored in a file named xxxxyyy.dat (where xxxx are the last four digits of the ID number, and the yyy are the first three letters of their last name) in other words, each applicants file will be uniquely named. the file containing the correct answers to questions is named ANSWERS.DAT
write a program that will read the contents of the ANSWERS.DAT file into an array (with the size of 20). program should read the applicants answer file into a second array (also 20) the logic of the program should the 'check' the applicants answer to a question and compare it to the 'correct' answer. the program should keep a tally of the number of questions correctly answerd, and the tally of incorrect answers. Finally the program should cout whether or not the applicant 'passed' or 'failed' the exam. they must answer at least 15 questions correctly to pass. program should indicate "PASS" or "FAIL" along with the number of INCORRECT and CORRECT.
following layout for program centered:
Department of Motor Vehicles
Driver's Exam
answered 99 questions correctly.
answered 99 questions incorrectly.
results for this portion of exam: XXXX
AND THATS ALL ALSO FOR AN EXAMPLE .DAT FILE '1278BOB.DAT' AND MULTIPLE CHOICE a,b,c,d
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See this[^] thread - we covered it all there.
Peter
"Until the invention of the computer, the machine gun was the device that enabled humans to make the most mistakes in the smallest amount of time."
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See here [^].
If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler.
-- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong.
-- Iain Clarke
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It's the weekend and the lazy assed homework seekers have started coming out of the woodwork. 
Doing my part to piss off the religious right.
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thanks for the response...
"could you if you could," help with a start on getting the two files into an array for comparison to get a 0 or 1 value and the add 1 to counter with printed results.? YOU'LL SEE ME GROW I'm new and will not give up.. eventually I'll have the chance to be knowledgeable and help lazy homeworkers. If not, could you point me to another person with a sense of humor.
project for c++ and need help. Source CODE IN C++
the word problem:
the department of motor vehicles administers a written driver's exam consisting of 20 multiple choice questions. an applicant for the drivers license exam answers these questions electronically and the answers are stored in a file named xxxxyyy.dat (where xxxx are the last four digits of the ID number, and the yyy are the first three letters of their last name) in other words, each applicants file will be uniquely named. the file containing the correct answers to questions is named ANSWERS.DAT
write a program that will read the contents of the ANSWERS.DAT file into an array (with the size of 20). program should read the applicants answer file into a second array (also 20) the logic of the program should the 'check' the applicants answer to a question and compare it to the 'correct' answer. the program should keep a tally of the number of questions correctly answerd, and the tally of incorrect answers. Finally the program should cout whether or not the applicant 'passed' or 'failed' the exam. they must answer at least 15 questions correctly to pass. program should indicate "PASS" or "FAIL" along with the number of INCORRECT and CORRECT.
following layout for program centered:
Department of Motor Vehicles
Driver's Exam
answered 99 questions correctly.
answered 99 questions incorrectly.
results for this portion of exam: XXXX
AND THATS ALL ALSO FOR AN EXAMPLE .DAT FILE '1278BOB.DAT' AND MULTIPLE CHOICE a,b,c,d
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Okay, just this once since you're a newbie.
Read ANSWERS.DAT into a 20x1 array. Read the applicant's answers into the first column of a 20x2 array. Step through both arrays, comparing the values in the first column. If they agree, set the corresponding element in the second column of the applicant's array to 1; if not, set it to 0. After comparing all 20 answers, sum the values of the applicant's array second column and cout the total as the number of correct answers.
As an algorithm, this should do it. For C++ help, you're on your own. It confuses the hell out of me, so I've given up trying to learn it. Programming rached its epitome with Pascal, and languages have been declining ever since.
"A Journey of a Thousand Rest Stops Begins with a Single Movement"
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johnzfrebbies@ wrote: I have a project for c++ and I need help for the first time. Source CODE IN C++
So why are you not asking ths question in a more appropriate forum?
"Love people and use things, not love things and use people." - Unknown
"To have a respect for ourselves guides our morals; to have deference for others governs our manners." - Laurence Sterne
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which one?
is there somewhere dedicated to tutoring help? or at least pointers in a correct direction?
I have a ways to go in my studies and knowledgable info is what I give in other areas of computer and OS technology, but in this language of c++ I find others perspectives to formulate algorithims more effecttive in learning and tuning to truely understand what I am doing. Some are wrong some are right but at least we all show a a meaningful insight with the best intentions at heart.
Thanks for at least being nice. John
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johnzfrebbies@ wrote: which one?
Here.
"Love people and use things, not love things and use people." - Unknown
"To have a respect for ourselves guides our morals; to have deference for others governs our manners." - Laurence Sterne
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I believe your stuck with me if thats okay  I've already be reprimanded for cross posting and I think you'll miss me if I go. I'll post there later to offer help or retain some helpful input. thanks for the tip.
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I think you should at least make an attempt at a solution and post the partial code. See the thread underneath this one where the poster displayed his work and asked for help in where he went wrong. By doing this it shows that you put some effort into the problem yourself rather than just passing the workload onto the other members of this website.
I have no problem in helping people that put effort into finding a solution. I'm not going to do somebody's homework, however.
And when the sunlight hits the olive oil, don't hesitate.
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sorry about that. I was in the process of working it out and not expecting a full blown finished product by any means. any ways thanks for pointing that out. heres what I have so far..... I can' t get my files to read in and compare.
#include "iostream"
#include "fstream"
#include "string"
#include "iomanip"
using namespace std;
int main()
{
int i, correct = -1, incorrect = -1;
ifstream StudentAnsw;
StudentAnsw.open("C:\\driversexam.dat");
ifstream Answers;
Answers.open("C:\\Answers.dat");
char StudentA[20], answer[20];
cout << "\t\t\tTHESE ARE YOUR RESULTS.\n";
for(i = 0; i < 20; i++)
{
cout <<"Question " << (i+1) << " " << endl;
Answers >> answer[i];
StudentAnsw >> StudentA[i];
if(StudentA[i] == answer[i])
{
//Answers >> answer;
//StudentAnsw >> StudentA;
cout << " Was answered correctly.\n";
correct++;
}
else
{
cout << StudentA[i] << " is an incorrect choice.\n";
incorrect++;
}
}
correct = correct++;
incorrect = incorrect++;
cout << "\t\t\tYou answered " << correct << " questions correctly.\n";
cout << "\t\t\tYou answered " << incorrect << " questions incorrectly.\n";
if (correct >= 15)
{
cout << "\n\t\t\tCONGRATUATIONS! \n\t\t\t\tYOU HAVE PASSED THE DRIVER'S LICENSE TEST.\n\a\a";
cout << "\t\t\t\tDON'T DRINK AND DRIVE" << endl;
}
else
{
cout << "\nSorry. You FAILED! the Driver's License Exam.\n";
cout << "\nYou need 15 correct answers to pass the exam.\n";
cout << "\nPlease Study and stay of the road. \n";
}
system("pause");
StudentAnsw.close();
Answers.close();
return 0;
}
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johnzfrebbies@ wrote: I can' t get my files to read in and compare.
So what's the problem?
johnzfrebbies@ wrote: correct = correct++;
incorrect = incorrect++;
Are you sure this is what you want?
"Love people and use things, not love things and use people." - Unknown
"To have a respect for ourselves guides our morals; to have deference for others governs our manners." - Laurence Sterne
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Hey thanks I corrected that and changed the counter to 0. but still can' read in files for comparison.
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Okay, your code seems correct. To be sure, I copied and compiled your program. For input I used the text file C:\driversexam.dat containing the numbers 1 to 20 and then in Answers.dat I also put the numbers 1 to 20, but I mixed a few up to simulate incorrect answers (Note: this will work with both numbers and characters).
It seems to work correctly.
Here is the output:
THESE ARE YOUR RESULTS.
Question 1
Was answered correctly.
Question 2
Was answered correctly.
Question 3
4 is an incorrect choice.
Question 4
3 is an incorrect choice.
Question 5
Was answered correctly.
Question 6
Was answered correctly.
Question 7
Was answered correctly.
Question 8
Was answered correctly.
Question 9
Was answered correctly.
Question 10
Was answered correctly.
Question 11
Was answered correctly.
Question 12
Was answered correctly.
Question 13
Was answered correctly.
Question 14
Was answered correctly.
Question 15
Was answered correctly.
Question 16
Was answered correctly.
Question 17
Was answered correctly.
Question 18
Was answered correctly.
Question 19
Was answered correctly.
Question 20
Was answered correctly.
You answered 18 questions correctly.
You answered 2 questions incorrectly.
CONGRATUATIONS!
YOU HAVE PASSED THE DRIVER'S LICENSE TEST.
DON'T DRINK AND DRIVE
Press any key to continue . . .
So it seems to work. Have you placed driversexam.dat and Answers.dat in C:\? You've hard-coded the directory structure, so make sure you have the files to be read in the right location. If not, maybe you could provide some more description regarding the problem.
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I don't under stand what I'm doing wrong?..please advise
#include "iostream"
#include "fstream"
#include "string"
#include "iomanip"
using namespace std;
int main()
{
int i;
//int x;
int correct;
int incorrect;
ifstream StudentAnsw;
ifstream Answers;
StudentAnsw.open("C:\\driversexam.dat");
Answers.open("C:\\Answers.dat");
char StudentA[20];
char answer[20];
cout << "THESE ARE YOUR RESULTS.\n";
correct = 0;
incorrect = 0;
for(i = 0; i < 20; i++)
{
cout <<"Question " << (i+1) << " " << endl;
Answers >> answer[i];
StudentAnsw >> StudentA[i];
if (StudentA == answer)
{
cout << " " << " Is a correct answer." << endl << endl;
correct++;
}
else
{
cout << " " << " Is a incorrect choice." << endl;
incorrect++;
}
}
system("pause");
system("CLS");
cout << "You answered " << correct << " questions correctly.\n";
cout << "You answered " << incorrect << " questions incorrectly.\n";
if (correct >= 15)
{
cout << "\nCONGRATUATIONS! \nYOU HAVE PASSED THE DRIVER'S LICENSE TEST.\n";
cout << "DON'T DRINK AND DRIVE" << endl;
}
else
{
cout << "\nSorry. You FAILED! the Driver's License Exam.\n";
cout << "\nYou need 15 correct answers to pass the exam.\n";
cout << "\nPlease Study and stay of the road. \n";
}
StudentAnsw.close();
Answers.close();
return 0;
}
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