Read coefficients of linear equations into 2d array
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Hi, I'm working on a program that reads linear equations from a file such as those:
3x+2y-2.5z=9
-2x+9y+12z=23.4
4.2x-7y+9.6z=45.3The file is supposed to contain n equations with n variables which I would read into a 2d dynamic array of doubles and then I'm supposed to solve the resulting matrix using Gauss's method. I've already implemented Gauss's method but I can't figure out when reading from file how to get only the numbers and the signs for example from the above equations I'm supposed to have the following in the array:
[+3][+2][-2.5]
[-2][+9][+12]
[+4.2][-7][+9.6]I need the numbers after the equal sign to be stored in a separate n sized array as well. If anyone has any ideas I'd really appreciate it :)
First read the file one line at a time. You could use ifstream::getline[^] for this. Then you could use the strtok_s function[^] to separate the coefficients.
«_Superman_» I love work. It gives me something to do between weekends.
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if i understood your problem correctly, then open the src file in read mode, open another dest file in write mode, copy character by character from src file to dest file. if any alphabet is read, then write some standard character like ':' or any other char which is not in your expressions. for example, 3x-2y+7z-3q=2.5 will become 3:-2:+7:-3:=2.5 then do something like fscanf("%f:",&el1); still some more logics we may have to implement like finding size of the 2d array etc. we can work around them subsequently if u have understood till here.
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I don't think so. First you don't need to create a file in order to read and parse an existing file. Second, there is no guarantee the variables are ordered the same in every line and/or a coefficient of zero gets mentioned at all, so one really has to check the variable names. All it takes is reading the characters of a line, then parse it into numbers, identifiers and operators. :)
Luc Pattyn [Forum Guidelines] [My Articles]
DISCLAIMER: this message may have been modified by others; it may no longer reflect what I intended, and may contain bad advice; use at your own risk and with extreme care.
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So maybe I'd read each line into a string, and then go through it char by char checking for letters and = and if not I'd store in the 2d double array and after I find a letter I move to the next column, and so on till the = and store what's after it in the solutions array. I'm getting a vague idea now of how to do this, but are the signs and decimal points also readable and convertible in the same way? For example when reading -2.9 , the - & . wouldn't fall in the range for the letters and the = but can I convert them along with the numbers into a double??
yes, that is about right, except you are not sure the variables will appear in the same order every time (one even could be omitted when its coefficient happens to be zero). So you must parse the line into numbers, identifier names and operators; then keep an array of known identifiers (=variable names) which leads you to the right column in the 2D matrix. :)
Luc Pattyn [Forum Guidelines] [My Articles]
DISCLAIMER: this message may have been modified by others; it may no longer reflect what I intended, and may contain bad advice; use at your own risk and with extreme care.
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I don't think so. First you don't need to create a file in order to read and parse an existing file. Second, there is no guarantee the variables are ordered the same in every line and/or a coefficient of zero gets mentioned at all, so one really has to check the variable names. All it takes is reading the characters of a line, then parse it into numbers, identifiers and operators. :)
Luc Pattyn [Forum Guidelines] [My Articles]
DISCLAIMER: this message may have been modified by others; it may no longer reflect what I intended, and may contain bad advice; use at your own risk and with extreme care.
Luc Pattyn wrote:
there is no guarantee the variables are ordered the same in every line
yes it is a valid point. even iam thinking in that perspective.i assumed the same sequence of variables while posting. let the op confirm this point, i.e. if the same sequence is guarenteed or not..
-------------------------------------------- Suggestion to the members: Please prefix your main thread subject with [SOLVED] if it is solved. thanks. chandu.
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yes, that is about right, except you are not sure the variables will appear in the same order every time (one even could be omitted when its coefficient happens to be zero). So you must parse the line into numbers, identifier names and operators; then keep an array of known identifiers (=variable names) which leads you to the right column in the 2D matrix. :)
Luc Pattyn [Forum Guidelines] [My Articles]
DISCLAIMER: this message may have been modified by others; it may no longer reflect what I intended, and may contain bad advice; use at your own risk and with extreme care.
I was just thinking about what would happen if a coefficient is zero and I just freaked out and thought I'd skip it before your reply :D But I'll try your way and see how it goes :) Thanks a lot :)
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First read the file one line at a time. You could use ifstream::getline[^] for this. Then you could use the strtok_s function[^] to separate the coefficients.
«_Superman_» I love work. It gives me something to do between weekends.
Yes I think I'll try getline() and save each line into a string in a string array, and then parse it like I was advised to do above and save the coefficients in the 2d array while checking for variable in the variable array each time. I think this would be the way to go :) Thanks for replying :)
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Luc Pattyn wrote:
there is no guarantee the variables are ordered the same in every line
yes it is a valid point. even iam thinking in that perspective.i assumed the same sequence of variables while posting. let the op confirm this point, i.e. if the same sequence is guarenteed or not..
-------------------------------------------- Suggestion to the members: Please prefix your main thread subject with [SOLVED] if it is solved. thanks. chandu.
No the sequence is not constant and there might be coefficients of 0 which would the variable would not be at all present in the line.
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No the sequence is not constant and there might be coefficients of 0 which would the variable would not be at all present in the line.
fine then, i will also work aroundit. as of now, do as luc pattyn suggested. if you get the solution please specify it here. otherwise i shall attempt it on monday. all the best.
-------------------------------------------- Suggestion to the members: Please prefix your main thread subject with [SOLVED] if it is solved. thanks. chandu.
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fine then, i will also work aroundit. as of now, do as luc pattyn suggested. if you get the solution please specify it here. otherwise i shall attempt it on monday. all the best.
-------------------------------------------- Suggestion to the members: Please prefix your main thread subject with [SOLVED] if it is solved. thanks. chandu.
OK then, thank you all for your help and I'll post here if I get it done :)
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OK then, thank you all for your help and I'll post here if I get it done :)
Hmm, How about a RegExp? You could scrub data into a tonenized string then convert it to an array. There is an open source mathematics program called 'sage', I would look atthe aproach they are implimenting. Also, you might find other good ideas by searching for OpenML. There are many examples supported by many frameworks.
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Yes I think I'll try getline() and save each line into a string in a string array, and then parse it like I was advised to do above and save the coefficients in the 2d array while checking for variable in the variable array each time. I think this would be the way to go :) Thanks for replying :)
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Hmm, How about a RegExp? You could scrub data into a tonenized string then convert it to an array. There is an open source mathematics program called 'sage', I would look atthe aproach they are implimenting. Also, you might find other good ideas by searching for OpenML. There are many examples supported by many frameworks.
I'll look into the source of 'sage' then and see if it's of any help. The other things you mentioned I'm afraid I don't understand as I am not a very advanced programmer (yet I hope :) ). Thanks for replying :)
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Oh yeah, forgot to mention another idea. Create a Red / Black tree from the code. Look at examples for expanding lambda expressions.
I don't know about this either, so I'll try working with the hints and ideas from above and if it doesn't work out I'll research this and work on it :) Thanks for your ideas :)
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I don't know about this either, so I'll try working with the hints and ideas from above and if it doesn't work out I'll research this and work on it :) Thanks for your ideas :)
hope your problem is solved. i did some paperwork onit yesterday and got some ideas. do you require any more discussion on that today?
-------------------------------------------- Suggestion to the members: Please prefix your main thread subject with [SOLVED] if it is solved. thanks. chandu.
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hope your problem is solved. i did some paperwork onit yesterday and got some ideas. do you require any more discussion on that today?
-------------------------------------------- Suggestion to the members: Please prefix your main thread subject with [SOLVED] if it is solved. thanks. chandu.
Actually I was very busy yesterday, so I didn't have time to implement the ideas that I got from the discussion here yet but I'll start working on it today and let you know how it works out. Post your ideas anyway they might help me now :) I need all the help I can get :) Thank you for taking the time to think about the problem :)
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Actually I was very busy yesterday, so I didn't have time to implement the ideas that I got from the discussion here yet but I'll start working on it today and let you know how it works out. Post your ideas anyway they might help me now :) I need all the help I can get :) Thank you for taking the time to think about the problem :)
so, kindly confirm these points for me as per my understanding of the problem. 1. the coefficients may be 0 means, one of the variables may be absent in the expression. 2. the sequence of the variables may change. 3. Will a variable be only 1 character or may be more? 4. what will be the maximum n? (size of expression/number of expressions) because, the solution i have sketched are dependant onthese inputs.
-------------------------------------------- Suggestion to the members: Please prefix your main thread subject with [SOLVED] if it is solved. thanks. chandu.
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Hi, I'm working on a program that reads linear equations from a file such as those:
3x+2y-2.5z=9
-2x+9y+12z=23.4
4.2x-7y+9.6z=45.3The file is supposed to contain n equations with n variables which I would read into a 2d dynamic array of doubles and then I'm supposed to solve the resulting matrix using Gauss's method. I've already implemented Gauss's method but I can't figure out when reading from file how to get only the numbers and the signs for example from the above equations I'm supposed to have the following in the array:
[+3][+2][-2.5]
[-2][+9][+12]
[+4.2][-7][+9.6]I need the numbers after the equal sign to be stored in a separate n sized array as well. If anyone has any ideas I'd really appreciate it :)
Omar Al Qady wrote:
If anyone has any ideas I'd really appreciate it
Here's a half-baked one:
void main( void )
{
char szTemp[16],
*pInput[3] = { "3x+2y-2.5z=9",
"-2x+9y+12z=23.4",
"4.2x-7y+9.6z=45.3" };int x = 0; double d1, d2, d3; for (char \*p = pInput\[0\]; p && \*p != '\\0'; p++) { if (isalpha(\*p)) { szTemp\[x\] = '\\0'; // use atof(szTemp) here x = 0; } else if ('=' == \*p) break; else { szTemp\[x\] = \*p; x++; } }}
"Old age is like a bank account. You withdraw later in life what you have deposited along the way." - Unknown
"Fireproof doesn't mean the fire will never come. It means when the fire comes that you will be able to withstand it." - Michael Simmons
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so, kindly confirm these points for me as per my understanding of the problem. 1. the coefficients may be 0 means, one of the variables may be absent in the expression. 2. the sequence of the variables may change. 3. Will a variable be only 1 character or may be more? 4. what will be the maximum n? (size of expression/number of expressions) because, the solution i have sketched are dependant onthese inputs.
-------------------------------------------- Suggestion to the members: Please prefix your main thread subject with [SOLVED] if it is solved. thanks. chandu.
1. Yes, that's possible, but a friend gave an idea of initializing the whole 2d array to equal zero, so when a variable isn't found in an equation the value isn't changed and would be correct for further calculations. 2. Yes, the sequence may change from one equation to another. 3. Variables could be one or more character so I'll just save them in an array of strings. 4. No maximum size was stated, but I don't think that matters as long as the arrays are dynamic, or does it?? :doh:
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1. Yes, that's possible, but a friend gave an idea of initializing the whole 2d array to equal zero, so when a variable isn't found in an equation the value isn't changed and would be correct for further calculations. 2. Yes, the sequence may change from one equation to another. 3. Variables could be one or more character so I'll just save them in an array of strings. 4. No maximum size was stated, but I don't think that matters as long as the arrays are dynamic, or does it?? :doh:
yes, my ideas seem to resemble with those you got yourself or my be from our friends here. go ahead, and you will surely achieve it. we will also co operate withyou.
-------------------------------------------- Suggestion to the members: Please prefix your main thread subject with [SOLVED] if it is solved. thanks. chandu.
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Omar Al Qady wrote:
If anyone has any ideas I'd really appreciate it
Here's a half-baked one:
void main( void )
{
char szTemp[16],
*pInput[3] = { "3x+2y-2.5z=9",
"-2x+9y+12z=23.4",
"4.2x-7y+9.6z=45.3" };int x = 0; double d1, d2, d3; for (char \*p = pInput\[0\]; p && \*p != '\\0'; p++) { if (isalpha(\*p)) { szTemp\[x\] = '\\0'; // use atof(szTemp) here x = 0; } else if ('=' == \*p) break; else { szTemp\[x\] = \*p; x++; } }}
"Old age is like a bank account. You withdraw later in life what you have deposited along the way." - Unknown
"Fireproof doesn't mean the fire will never come. It means when the fire comes that you will be able to withstand it." - Michael Simmons
Good ideas, I'll try to incorporate them into my solution :) Thanks :)