Quick Question about Excel Charts

sdcrym · 02-18-03, 09:41 PM

I have a function ( y = f(x) ) that I want to graph in Excel in an xy scatter plot. I usually just make a column of x values and then a column for the y values as a function of the first column, then make the plot based on this set of about 20 points. Is there any way to make a plot straight from the equation, like you would in a graphing calculator?

I hope I'm making myself clear, but if not, let me know and I'll try to elaborate. The function isn't of the type that can have a trend line or polynomial fit, so I can't just do the regression and use that as the function.

I guess I might as well put the equation I'm using:

y = a*x/(1+(a-1)*x) where 'a' is a known constant

BigPete · 02-18-03, 10:51 PM

In short, no ... not to my knowledge. Your only hope would be to generate a crapload of points and the try to get excel to apply the right trendline to it so it would return the original equation. I don't think it can create something in that form, though.

sdcrym · 02-18-03, 10:53 PM

That's what I figured, but thanks anyway. I was just curious

BigPete · 02-18-03, 10:58 PM

Quote:

Originally posted by sdcrym
That's what I figured, but thanks anyway. I was just curious

Yeah, I guess I didn't really bother to read past your first sentence or I would have known you knew all that and I could have just said 'no' ... oops.

tanman · 02-19-03, 12:26 AM

Actually I really need help too and was about to start my own thread. I need to make a graph using specific plot points (x,y) and need to find the linear equation of the best fit line y=mx+b how do I do that?

Its for chemistry. I'm plotting a standard curve for a Bradford and BCA assay in order to find the concentration for an unknown sample. If you were curious.

sdcrym · 02-19-03, 01:44 AM

Well, my response to you depends on how much you know about Excel already. In short, highlight the x and y columns in a spreadsheet, click the make chart button, select xy scatter. Make sure the next page has the x's and y's in the right place. I'm leaving out a lot of details, but you should be able to figure it out. After the scatter plot is displayed, right click on a data point and select add trendline. Make sure linear is selected, then move over to the options tab and check the display equation box.

Sorry for the incoherence... I just finished up my homework and now I'm off to bed

tanman · 02-19-03, 08:29 PM

Thank you very much! your help is much appreciated. I could figure it out.

02-18-03, 09:41 PM	#1
sdcrym DVD Talk Special Edition Join Date: Jan 2001 Location: Starkville, MS Posts: 1,657	Quick Question about Excel Charts I have a function ( y = f(x) ) that I want to graph in Excel in an xy scatter plot. I usually just make a column of x values and then a column for the y values as a function of the first column, then make the plot based on this set of about 20 points. Is there any way to make a plot straight from the equation, like you would in a graphing calculator? I hope I'm making myself clear, but if not, let me know and I'll try to elaborate. The function isn't of the type that can have a trend line or polynomial fit, so I can't just do the regression and use that as the function. I guess I might as well put the equation I'm using: y = ax/(1+(a-1)x) where 'a' is a known constant

02-18-03, 10:51 PM	#2
BigPete DVD Talk Hall of Fame Join Date: Oct 1999 Location: not CT Posts: 9,479	In short, no ... not to my knowledge. Your only hope would be to generate a crapload of points and the try to get excel to apply the right trendline to it so it would return the original equation. I don't think it can create something in that form, though. __________________ "What, are you kidding? Leviticus is an action packed thrill a minute! From the beginning where the lord tells Moses how to properly sacrifice animals (with much talk of blood and killing and the word "asunder" used a couple of times), to the very end where he's telling Moses what the value of a human being is, insofar as how much he should give to priests. And the bit in the middle about how everyone should keep their clothes on? Wow, just WOW, that's all I have to say." -Otto

02-18-03, 10:53 PM	#3
sdcrym DVD Talk Special Edition Join Date: Jan 2001 Location: Starkville, MS Posts: 1,657	That's what I figured, but thanks anyway. I was just curious

02-19-03, 12:26 AM	#5
tanman DVD Talk Ultimate Edition Join Date: Jan 2001 Location: Gator Nation Posts: 4,553	Actually I really need help too and was about to start my own thread. I need to make a graph using specific plot points (x,y) and need to find the linear equation of the best fit line y=mx+b how do I do that? Its for chemistry. I'm plotting a standard curve for a Bradford and BCA assay in order to find the concentration for an unknown sample. If you were curious.

02-19-03, 01:44 AM	#6
sdcrym DVD Talk Special Edition Join Date: Jan 2001 Location: Starkville, MS Posts: 1,657	Well, my response to you depends on how much you know about Excel already. In short, highlight the x and y columns in a spreadsheet, click the make chart button, select xy scatter. Make sure the next page has the x's and y's in the right place. I'm leaving out a lot of details, but you should be able to figure it out. After the scatter plot is displayed, right click on a data point and select add trendline. Make sure linear is selected, then move over to the options tab and check the display equation box. Sorry for the incoherence... I just finished up my homework and now I'm off to bed

02-19-03, 08:29 PM	#7
tanman DVD Talk Ultimate Edition Join Date: Jan 2001 Location: Gator Nation Posts: 4,553	Thank you very much! your help is much appreciated. I could figure it out.