Plot problem

[Sergey]

Hello!

There is something wrong with the plot of the function (look at the attached file).

When "x" is defined from 0 to 10 the plot looks correct. But when I define "x" from -10 to 10 plot looks like a straight line.

Where did I make a mistake during the plot?

Best regards,

Sergey

[DJNewman · Accepted solution]

You should define x as -10, -9 ... 10 instead of -10, 1...10.

Edit: Alternatively just write it as -10 ... 10 if you want your step size to be 1.

https://support.ptc.com/help/mathcad/r8.0/en/index.html#page/PTC_Mathcad_Help/range_operators.html

[StuartBruff]

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@Sergey wrote:

Hello!

There is something wrong with the plot of the function (look at the attached file).

When "x" is defined from 0 to 10 the plot looks correct. But when I define "x" from -10 to 10 plot looks like a straight line.

Where did I make a mistake during the plot?

Best regards,

Sergey

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Hi Sergey.

Your problem arises because you have (I think) used your intended step size in the range variable x's definition.

A range is defined as first_value,next_value..final_value. Mathcad uses the first and next values to calculate the step size.  You have x:=-10,1,10.  Consequently, Mathcad thinks you want x taking the values 10 and 1 (the next value after 1 would be 12, but the max range value you've give is 10).  What you want is x:= -10,-9..10.

Revised Mathcad Prime 8 worksheet attached.

Stuart

[Sergey]

Hello Stuart.

It seems that you are right. I simply misunderstood how to define the step and the range.

Now it is clear.

Thanks a lot.

Best,

Sergey

[StuartBruff]

No worries, Sergey.   It's a common Mathcad error, particularly when people have some familiarity with languages that use steps instead of the next value in the sequence.

Sometimes, it's useful to have the choice, so I have a library of sequence generation functions in my default worksheet.

You could even define a function - range, say - that generates a range using the first, next .. final specification:

Mathcad Prime 7 worksheet attached - it should work in Mathcad Express 7 and Mathcad Prime/Express 8, as well.

Stuart

[Sergey]

Thank you, Stuart.

I will study your sheets.

I think that my "old" definition of the range and step, that originated in the original problem of this thread, came from Matlab. 

Sergey

[StuartBruff]

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@Sergey wrote:

Thank you, Stuart.

I will study your sheets.

I think that my "old" definition of the range and step, that originated in the original problem of this thread, came from Matlab. 

Sergey

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Hi Sergey.

I wondered if Matlab's colon operator featured somehow - it's been a long time since I used it, though.   As noted in the description, the function linspace gives (or should give) the same results as Matlab's linspace.

An important point to note is that a range variable is a variable that contains a range (specification)- it does not contain the expanded definition and is *not* a vector (this causes a lot of confusion amongst new Mathcad users).   It's better to think of a range (first, next..last) as an implicit iterator rather than a vector.

Consequently, although linrange and range may look like they're doing the same thing, they are quite distinct.   linrange returns a vector, whilst range returns a range.

Stuart