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44 34 2 1
Message 21 of 34
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I can't look at it now, but I will later, and let you know what happened.  Best, 

Elad

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Message 22 of 34
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Well that last excellent idea of yours worked fine; no surprise there.  But I have not been able to create a matrix in CAS in which one of the elements is a variable.  

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Message 23 of 34
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This is one of the ways to solve it.

m2 is the RREF matix, and its element (2,4) is the solution for y.

Because y =0 this element has to be 0.

So we solve m2(2,4)=0 for u2.

 

Because we are dealing with complex numbers we use csolve.

The solution is the same as yours, but the exaxt one.

 

2017-08-23 12.29.25.jpg

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44 34 2 1
Message 24 of 34
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Thank you Jan for your input, but as I'm rather new to this calculator, I'm not understanding you.

 

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Level 6
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Message 25 of 34
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What is the first thing you do not understand?

 

I do a guess: you do not understand what := means.

 

Well, a:=3 has the same meaning as 3 ►a, so both instructions store 3 into variable a.

 

Personally I like the first notation better.

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Message 26 of 34
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@EladLending wrote:

  ......But I have not been able to create a matrix in CAS in which one of the elements is a variable.  


I can think of 2 reasons for that.

 

The first is not very probable, but it could be that the variable you want to use has already been assigned a value before, and for this reason is no abstract variable anymore.

 

I hope you are using lowercase variables and you could look in the memory manager( Shift - B) if it is present anywhere, or check your variables in Home and CAS. (Vars key)

 

Another reason could be that the Spreadsheet app is at the background, so the title in the blue bar on top of the screen reads: Spreadsheet.

 

Suppose that, with the Spreadsheet at background, you enter cd12 in CAS, then you see: 0 !

Why?

The CAS thinks that you mean the content of cell CD12 in the Spreadsheet, which is 0 !

 

So you always have to take this into account.

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44 34 2 1
Message 27 of 34
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Jan, ok I think I understand, but,  I must be doing something wrong.  Why is it not working?

 

Screenshot (20).png

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44 34 2 1
Message 28 of 34
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No, neither of those.  Just to make sure, I purged the variable (there was no variable).  And it's not in spreadsheet app.  Why, when I enter the elements of the matrix in CAS mode, do I see those little plus\minus signs?  They are not present in the screenshot you sent me.  

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Message 29 of 34
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Your matrix should look like this:

 

2017-08-23 22.41.35.jpg

 

You see that this is a 3*4 matrix, and I could add more rows or columns by tapping the +/- signs and entering new values

When I do this new +/- signs are automatically created to add even more rows or columns.

 

These +/-  signs are only needed for editing, and disappear after entering.

 

You have not created more columns by tapping these signs, but have a

3*1 matrix with impossible entries, like 2*i  u2.

This is not accepted by the CAS.

 

You could also go to Home settings and change Textbook towards Algebraic.

 

In this view your matrix should look like [[a,b,c,d],[e,f,g,h],[i,j,k,l]]

So there have to be comma's everywhere.

 

Probably you have used the space key as separator.

Instead of tapping the +/- signs you could also have used the comma for creating extra columns

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Message 30 of 34
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You guessed correctly again, Jan.  I WAS using the spacebar as a delineator. But by using (the invisible!!) commas I was able to replicate your results, and, yes, I got the correct solution for u2!  Halleluya!  Major progress. The calculator has solved for a variable located in the column where the constants usually reside.  Amazing.  But please, if you don't mind, I'm not sure I understand the last command entered: 

 

csolve(m2(2,4)=0,u2)

 

My interpretation is:

 

"Solve for the variable u2, given that the element located at row 2, column 4 in matrix m2 = 0."  

 

Is that correct?

 

Thank you again Jan, and Joe.  Both of you have be a tremendous help! 

 

(Sorry to be so dense....)

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