To make a graph

users
#1

Hi all:

         Would you please help me with this problem:

I have this set of data:

U A

1.37 13680

1.31 14000

I've tried to graph these data that show two lines, first 1.37 with 13680 and 1.31 with 14000, in the same graph. I want that the graph show where the lines intersect. And I prefer that A go in X axis and U in Y axis.

I couldn't do it yet. I put the data in some orders but I can get the graph.

Thanks in advance,

Regards,

Jorge Rodríguez

#2

Hi Jorge,

your question is not clear. To draw one line you need:
(1) The coordinates of two points, which makes four values
or
(2) The coordinates of one point and the slope

It is not clear, what meaning you values have.

Kind regards
Regina

jorge Rodríguez schrieb:

#3

I have this set of data:
U A
1.37 13680
1.31 14000

I've tried to graph these data that show two lines, first 1.37 with 13680 and 1.31 with 14000, in the same graph.

Sorry, but this makes no sense. Each pair of value here defines a point, not a line. There are an infinity of lines that you can draw through any point, having all possible gradients.You need at least two points to define a line, and then only on the assumption that the line is straight.

I want that the graph show where the lines intersect.

The infinity of possible lines through each of your two points intersect in a infinity of places. The question is not well enough defined to be answered. From your knowledge if the quantities that you are plotting, could you assume that both graphs go through the origin, (0,0)? If so, you could include these points and create two lines. But the answer to your query would then be trivial: the lines cross at (0,0)!

And I prefer that A go in X axis and U in Y axis.

That's easy: just reverse the order of your columns of data. It is very easy to move or copy data.

I couldn't do it yet. I put the data in some orders but I can get the graph.

That's because - with only one point in each set of data - there is no graph to get.

I trust this helps.

Brian Barker

#4

Hi :slight_smile:
Dohh, I sent this as a pm rather than to the whole list. So I've had to
forward it.

I still don't understand why we want to push people's replies off-list.
Off-list means the replies are not subject to peer review and makes it
difficult to know whether a question has been resolved or not and it's
impossible to look back over old solutions that may still work.

Hey ho, grumble done :wink:
Regards from a
Tom :slight_smile:

#5

Hi Regina and Brian:

         Thanks for your answer. Excuse me because I haven't been clear with my explanation.

         Below you can find a link to access a file were I draw manually the graph that I need to do:

         https://www.dropbox.com/s/7oqptiz8e6r9gxi/Graph.pdf?dl=0

Regards,

Jorge Rodríguez

#6

Hi Jorge,

jorge Rodríguez schrieb:

Hi Regina and Brian:

        Thanks for your answer. Excuse me because I haven't been clear
with my explanation.

        Below you can find a link to access a file were I draw manually
the graph that I need to do:

        https://www.dropbox.com/s/7oqptiz8e6r9gxi/Graph.pdf?dl=0

That is clear now.

Make your entries in the sheet like this:

A U
Line 1
13680 0
0 1.37
Line 2
14000 0
0 1.31

Mark the range from "Line 1" to "1.37" and generate an XY-Chart. At step 3 in the wizard click on button Add. Now go through the roles in the top, right part "Data Ranges" and enter the range in the field "Range for ...". You can minimize the dialog and click on the cell.

In case you have entered the data starting in cell A1, you would get for Line 1

Name $A$2
X-Values $Sheet1.$A$3:$A$4
Y-Values $Sheet1.$B$3:$B$4

and for Line 2
Name $A$5
X-Values $Sheet1.$A$6:$A$7
Y-Values $Sheet1.$B$6:$B$7

You should enable all kind of grid and reduce the line width of the data series. That makes it easier to estimate the intersect values.

I would not do it in Calc, but I would do it in GeoGebra, where you can construct the interaction point and get the coordinates directly. In contrast to a TI-nSpire or similar, GeoGebra is free, see https://www.geogebra.org/

Kind regards
Regina

#7

So your data set is actually:
A U1 U2
0 1.37 1.31
13680 0
14000 0
(with some missing values).

You will have seen Regina Henschel's recipe for a graph. Here is another:
o Select the data block as above and click the Chart button.
o Select "X-Y (Scatter)" and leave all other options as default.
o Select the chart (grey border, not coloured handles).
o Right-click a point and select Insert Trend Line... and OK.
o Repeat for a point on the other line.

But do you really want to see the graph, or perhaps just find the coordinates of the point of intersection, as was perhaps hinted at by your original request? Application of similar triangles shows that the U coordinate of the point of intersection is given by
1.31 * 1.37 * (14000 - 13680) / (1.37 * 14000 - 13680 * 1.31)
and that the A coordinate is
14000 * ( 1 - U / 1.31)
- where U is the U coordinate calculated above.

You will see that these give the intersection point as A=9126, U=0.456.

I trust this helps.

Brian Barker

#8

Hi Brian:

         As I said to Regina, thank you very much for your explanation. I could reproduce the graph as you instructed to me.

         I found both graph clear and making what I need.

         Yes, I need the graph and the coordinates of the interception both lines too. I follow your equation to find U, and I reproduced it well with the same result. But I tried to do the same with A coordinate interception: 14000 * ( 1 - U / 1.31 ) and I got : 5813 not 9126. As you said, 9126 is the correct point where intercept but I couldn't get in my calculation. Would you please, tell me what would I do wrong ?

Regards,

Jorge Rodríguez

#9

As I said to Regina, thank you very much for your explanation.

No probs!

I could reproduce the graph as you instructed to me. I found both graph clear and making what I need.

Good-oh!

Yes, I need the graph and the coordinates of the interception both lines too. I follow your equation to find U, and I reproduced it well with the same result. But I tried to do the same with A coordinate interception: 14000 * ( 1 - U / 1.31 ) and I got : 5813 not 9126. As you said, 9126 is the correct point where intercept but I couldn't get in my calculation. Would you please, tell me what would I do wrong ?

You seem to have calculated 14000 * ( 1 - U ) / 1.31 instead of 14000 * ( 1 - U / 1.31 ) - which means 14000 * ( 1 - ( U / 1.31 ) ), of course.

Brian Barker

#10

Thank you Brain, I could do it now well and got the same result : 9126

Regards,

Jorge Rodríguez

#11

Thank you Brain, ...

I may be bright, but there is no need to call me that!

I could do it now well and got the same result : 9126

Good-oh!

Brian Barker