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simple divide error

ptc-5431457
1-Newbie

simple divide error

i'm doing something wrong. please help.

1. i assign values to variables "C2" & "fc"

2. i multiply the variables * 2 pi and assign the expression to another variable "test". expression value is correct. in this case is 0.022.

3. i try to divide 1/test and get 46.125. wrong answer

i tried parenthesis around expression = 46.125

i tried inverse test^-1 = 46.125

4. if i just type 1/.022 = 45.455. right answer.

is there a tolerance i need to set? CTOL and TOL don't fix it.

is there syntax i'm missing?

this is part of a much larger constraints i'm trying to solve. 2 equations 2 unknowns. when i use the expression i get no solution. when i type the value of the expression the solver gets pretty close to the correct solutions.

3 REPLIES 3

i see symbolics test -> 0.021680130902423163, which then equals 46.125. how do control this precision? truncate or equivalent?

In prime 2 the method is :

1. select the result

2. select formatting on the top (tab) menu.

3. below the formating tab you have 3 choices

format

precision

complex

select the precision by clicking on it & it gives a drop down choice.

increase the number of digits to suit your need by single click on the required value

I expect that prime 3 will be the same

Regards

Andy

Its absolutely unclear to me why you think that 45.455 should be the correct result!

"test" is calculated using a number with 16 decimals (C2) and an irrational number (pi) - you don't think the result is exactly 0.022, don't you?

How to control the displayed decimals with numeric evaluation was shown by Andy. These settings only affect the display of the result, not the precision of the calculation.

You may use the modifier "float" with symbolic evaluation, but you shouldn't. The reason is that this setting will also affect the precison of all internal calculations. In Mathcad15 and below we could format the result of symbolic evaluations the same way as we could for numericals, but in Prime we can't.

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