Is it possible to recall expression on TI-Nspire?
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Marcin W
Nov 11, 2016, 5:44:53 AM11/11/16
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Hi.
I am using TI-NSpire CX CAS with OS 4.3, and I'm trying to work with expressions. For example (on empty and clean new document):
a * sin(x) -> y
1 -> a
And now, if I want to use y:
y
(result): sin(x)
It is all OK - y is recalculated and simplified as it should be.
My question is: how to recall expression of y? On TI-89 there were two possibilities: select "Contents" (F6) on VAR-LINK and RCL command (2ND + STO>). RCL is prefered way because we can now do everything we want with recalled expression, in particular we can modify it. On TI-Nspire we can only recall programs and functions, not expressions.
It is possible to check that value of y still is a * sin(x):
DelVar a
y
(result): a * sin(x)
Of course it is not acceptable way-around because I do not want to delete my important variables, and, in fact, I even don't know which variables to delete, because i have no information about y is using some a! As stated erlier:
y
(result): sin(x)
So: why Menu/Actions/Recall definition only allows to recall functions and program, not expressions on TI-Nspire? Is there any way to recall expression stored in y?
I am using TI-NSpire CX CAS with OS 4.3, and I'm trying to work with expressions. For example (on empty and clean new document):
a * sin(x) -> y
1 -> a
And now, if I want to use y:
y
(result): sin(x)
It is all OK - y is recalculated and simplified as it should be.
My question is: how to recall expression of y? On TI-89 there were two possibilities: select "Contents" (F6) on VAR-LINK and RCL command (2ND + STO>). RCL is prefered way because we can now do everything we want with recalled expression, in particular we can modify it. On TI-Nspire we can only recall programs and functions, not expressions.
It is possible to check that value of y still is a * sin(x):
DelVar a
y
(result): a * sin(x)
Of course it is not acceptable way-around because I do not want to delete my important variables, and, in fact, I even don't know which variables to delete, because i have no information about y is using some a! As stated erlier:
y
(result): sin(x)
So: why Menu/Actions/Recall definition only allows to recall functions and program, not expressions on TI-Nspire? Is there any way to recall expression stored in y?
Mark Arguijo
Nov 11, 2016, 7:16:46 AM11/11/16
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Try choosing y from the variables key (VAR). I think that should recall it for you.
Mark Arguijo
Mark Arguijo
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Marcin W
Nov 11, 2016, 7:23:33 AM11/11/16
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Yes, it recalls but only name, not expression stored in it. After
selecting "y" in VAR it is put into entry line as y (name), and after
pressing ENTER I get simplified value, not actual expression stored in
y.
But thanks for help!
Regards
Marcin
selecting "y" in VAR it is put into entry line as y (name), and after
pressing ENTER I get simplified value, not actual expression stored in
y.
But thanks for help!
Regards
Marcin
Message has been deleted
Mark Arguijo
Nov 11, 2016, 7:54:12 AM11/11/16
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What if you delete the a variable? Delvar a. And they try y..
Mark Arguijo
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Mark Arguijo
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Marcin W
Nov 11, 2016, 8:03:42 AM11/11/16
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W dniu piątek, 11 listopada 2016 13:54:12 UTC+1 użytkownik Mark Arguijo napisał:
What if you delete the a variable? Delvar a. And they try y..
I have already written about that in my first post. It is no solution - I don't want to delete my variables just to see one expression stored in another. And, as stated erlier: I even do not know which variables to delete because I don't know which variables are used in expression - i have to delete ALL of them!
Dennis Donovan
Nov 11, 2016, 8:59:31 AM11/11/16
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Once you define a letter in an expression, the value becomes incorporated in the definition of the expression, but you can change the value of the letter and see the new expression definition with the new value by typing "y" on the calculator page. If you want the see the original definition of the expression with letters, then you can do the definition on a notes page or a graphs page (as a function). I have attached a simple document with a Calc, Notes and Graph page, notice on the Graphs and Notes pages, the original expression definition is left intact and then the current expression is shown based on the value of the coefficient.
Not sure if this is what your looking for, but it is a way to see the original definition.
P.S. The Ctrl Var (->) way to define elements is a legacy function (and is useful on a graphs page to store variables calculated there), but the new way to define things is using the := on the TI-Nspire, I demonstrated both on the notes page.
From: Marcin W <wir...@gmail.com>
To: tinspire <tins...@googlegroups.com>
Sent: Friday, November 11, 2016 5:44 AM
Subject: [tinspire] Is it possible to recall expression on TI-Nspire?
Marcin W
Nov 11, 2016, 11:27:46 AM11/11/16
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Hm, thank You ddhawk1, i really appreciate Your help, but it is getting strange.
What i want is just to do some calculations using expressions - fundamental objects in math. On my TI-89 everything work as expected: I can define expressions (as names, "expression variables"), use it (calculate and simplify), and modify it (using RCL) as I need. These all are basic operations which I consider fundamental for calculating something using calculator. But it looks like on TI-Nspire i have to use other applications just to make something like side-notes, because calculator (Calculator App) does not provide possibility to check or modify expressions it has stored in memory. But operating expressions is essential for Calculator App to exist!
Aand even if I define some expressions in Notes App what about expressions received as results?
Another example:
DelVar a
f := a * sin(x)
g := integral(f, x) <- g is not defined in any other App, i have just calculated that!
... later
a := 1
... later
g
(result): -cos(x)
In fact, definition of g is: -a * cos(x)
And there is no way to recall true expression of g without deleting varable a, and maybe other variables - it is not known what variables g may be using.
I am really bad surprised it is not possible to recall definition of stored expresson just by using Actions/Recall definition, like on TI-89. For now it looks like there is no other option but makig side-notes for every expression, particullar result expressions.
What i want is just to do some calculations using expressions - fundamental objects in math. On my TI-89 everything work as expected: I can define expressions (as names, "expression variables"), use it (calculate and simplify), and modify it (using RCL) as I need. These all are basic operations which I consider fundamental for calculating something using calculator. But it looks like on TI-Nspire i have to use other applications just to make something like side-notes, because calculator (Calculator App) does not provide possibility to check or modify expressions it has stored in memory. But operating expressions is essential for Calculator App to exist!
Aand even if I define some expressions in Notes App what about expressions received as results?
Another example:
DelVar a
f := a * sin(x)
g := integral(f, x) <- g is not defined in any other App, i have just calculated that!
... later
a := 1
... later
g
(result): -cos(x)
In fact, definition of g is: -a * cos(x)
And there is no way to recall true expression of g without deleting varable a, and maybe other variables - it is not known what variables g may be using.
I am really bad surprised it is not possible to recall definition of stored expresson just by using Actions/Recall definition, like on TI-89. For now it looks like there is no other option but makig side-notes for every expression, particullar result expressions.
Mark Arguijo
Nov 11, 2016, 12:47:43 PM11/11/16
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How about this.....
Save a*sin(x) as a string in y.
Save the value 1 in a.
Save expr(y) in y1.
Now when you type y1, it returns the evaluated value. To get the original expression back, type y.
See pic below:
See pic below:
Mark Arguijo
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Regina Henschel
Nov 11, 2016, 1:57:16 PM11/11/16
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Hi Marcin,
how different views are. If I want to make something depend on variable
a and x, I define a function for it. My way would be
f(a,x):=a*sin(x)
and then use f(1,x) in case the value of a is 1.
Kind regards
Regina
Marcin W schrieb:
how different views are. If I want to make something depend on variable
a and x, I define a function for it. My way would be
f(a,x):=a*sin(x)
and then use f(1,x) in case the value of a is 1.
Kind regards
Regina
Marcin W schrieb:
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Marcin W
Nov 11, 2016, 3:52:46 PM11/11/16
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Mark:
Right, maybe it is some kind of solution, but i would consider it as a hack - it is not comfortable for day by day use. For me TI calculators are rather devices which helps me doing math, not devices which I have to hack to do math ;)
And solution is so simple: just allow to select expressions in Menu/Actions/Recall definition...
Regards
Marcin
Right, maybe it is some kind of solution, but i would consider it as a hack - it is not comfortable for day by day use. For me TI calculators are rather devices which helps me doing math, not devices which I have to hack to do math ;)
And solution is so simple: just allow to select expressions in Menu/Actions/Recall definition...
Regards
Marcin
Marcin W
Nov 11, 2016, 3:53:35 PM11/11/16
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Regina, You are right - I may use functions. But there are two things:
First thing:
First thing:
Expressions in day by day use are in many situations just better and more comfortable than functions. We can simply write:
f := a * sin(x)
g := integral(f, x)
g
(result): -a * cos(x) <- and it is definition of g, we can't recall this in this form on TI-Nspire if we later define a.
At this point any change to f has no impact on g.
Using functions:
f(x) := a * sin(x)
g(x) := integral(f(x), x)
g(x)
(result): -a * cos(x)
Looks good! BUT if we now recall definition of g(x) we get this:
Define g(x) = integral(f(x), x)
g(x) is not calculated integral of f(x) - it is how to GET integral of f(x)
Graphing such g(x) in many situations is order of magnitude slower than just drawing calculated integral. But not only graphing, every later expression that uses g(x) in fact calculates this integral. Event more: if we now change definition of f(x), g(x) changes also - now it will be integral of NEW f(x).
And it is ok, functions are just another beasts than expressions - no problem here. The problem is Second thing:
Second thing:
This problem is more inherent: expressions are fundamental objects in math, TI calcs supports it for years, and allows to store them as "expression variables". Expressions were never some kind of "strange things" or unwanted children... until TI-Nspire. Now we can define expressions but, after that, we can not check what have we defined (or sometimes even check what has been calculated if result is expression stored to expression variable) - it is not a mathematical behavior. There should be symmetry: define <-> recall definition - it is mathematics at all! Expressions on TI calculators just started to be write-only.
Wow ;)
Regards
Marcin
(result): -a * cos(x) <- and it is definition of g, we can't recall this in this form on TI-Nspire if we later define a.
At this point any change to f has no impact on g.
Using functions:
f(x) := a * sin(x)
g(x) := integral(f(x), x)
g(x)
(result): -a * cos(x)
Looks good! BUT if we now recall definition of g(x) we get this:
Define g(x) = integral(f(x), x)
g(x) is not calculated integral of f(x) - it is how to GET integral of f(x)
Graphing such g(x) in many situations is order of magnitude slower than just drawing calculated integral. But not only graphing, every later expression that uses g(x) in fact calculates this integral. Event more: if we now change definition of f(x), g(x) changes also - now it will be integral of NEW f(x).
And it is ok, functions are just another beasts than expressions - no problem here. The problem is Second thing:
Second thing:
This problem is more inherent: expressions are fundamental objects in math, TI calcs supports it for years, and allows to store them as "expression variables". Expressions were never some kind of "strange things" or unwanted children... until TI-Nspire. Now we can define expressions but, after that, we can not check what have we defined (or sometimes even check what has been calculated if result is expression stored to expression variable) - it is not a mathematical behavior. There should be symmetry: define <-> recall definition - it is mathematics at all! Expressions on TI calculators just started to be write-only.
Wow ;)
Regards
Marcin
Mark Arguijo
Nov 11, 2016, 4:20:15 PM11/11/16
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I think the problem is that you are confusing expressions with strings.
You are correct that when you define a function, it should return the function. The problem you are having is that once you define the variable a, it is replaced in your function definition. Therefore, when you ask it to return the function value, it does (with all defined variables replaced with their values).
If you define a string variable and then tell the Nspire to treat this string as an expression (this is what the expr() does), it does not change the defined string but rather converts to an expression with all defined variables replaced.
This may not make "mathematical" sense but from a coding point of view, its natural.
I'm sorry that I couldn't come up with a nice, elegant solution for you but I don't see it as a hack but rather demonstrating how the Nspire treats different data types.
Your original problem was looking up what you had originally defined y to be. If you define y:=string variable, you will always be able to see its definition. If you would like to evaluate with y, then you can convert it to an expression with expr(). Your can perform mathematical calculations with expressions, not strings..
Juan my two cents. Good luck!!
Regards,
Mark
Mark
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Marcin W
Nov 11, 2016, 5:30:04 PM11/11/16
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Mark, You are right - your solution is ok and it will work. maybe calling it "a hack" was little misfortunate, i am really sorry.
But my original problem was how to recall definition of expression stored as expression variable. You proposed to store expressions in strings - it may be very good in this situation.
And now the problem is: why we have to consider solutions which require expr() on expressions converted to strings (loosing pretty print and many other editing and expression manipulation features) on a mathematical machine that can calculate integrals, differential equations, graph colorfull graphs, do financial calculations I have never mind about, and even check if e^(i*pi)=-1, but just can not recall stored in memory definition of mathematical expression? This rocket-science technology was implemented in TI-89 in 1998. I am sorry, I can not reconcile with it yet ;)
So, it looks to mi like a bug. I don't know, maybe some TI people read this group?
Regards
Marcin
But my original problem was how to recall definition of expression stored as expression variable. You proposed to store expressions in strings - it may be very good in this situation.
And now the problem is: why we have to consider solutions which require expr() on expressions converted to strings (loosing pretty print and many other editing and expression manipulation features) on a mathematical machine that can calculate integrals, differential equations, graph colorfull graphs, do financial calculations I have never mind about, and even check if e^(i*pi)=-1, but just can not recall stored in memory definition of mathematical expression? This rocket-science technology was implemented in TI-89 in 1998. I am sorry, I can not reconcile with it yet ;)
So, it looks to mi like a bug. I don't know, maybe some TI people read this group?
Regards
Marcin
Earl Whitney
Nov 11, 2016, 7:08:22 PM11/11/16
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I am a little late to the party, but here's an idea. I have not read everyone's solutions, and I am new to the group, so please forgive me if my solution is superfluous.
In a document, define the function on a graphs page. Then use the function name from the graphs page elsewhere. You can always go back to the graphs page to see the function expression.
Best wishes,In a document, define the function on a graphs page. Then use the function name from the graphs page elsewhere. You can always go back to the graphs page to see the function expression.
Earl
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John Hanna
Nov 11, 2016, 9:07:37 PM11/11/16
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1. I would prefer you define y(x):=a*sin(x)
2. Use y(x)|a=1 instead of 1->a.
This preserves y(x).
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