Exressions question?

[67SS509]

When entering your expression in the calc.pid which is correct....

"({EXT.AD1}*2.5)+8.75"
or
"{EXT.AD1}*2.5+8.75"

or does it matter?

This is for a FJO wideband with a .5v-4.5v analog output= 10-20AFR

[joecar]

The operator * has higher precedence than the operator + so both expressions are the same.

See the scantool user manual, page 92.

[mr.prick]

It should have the brackets. IMO
Some of the WBO2 PIDs are missing them.

calc_pids will have improper data
if the equation is not strung together properly.

[joecar]

Show me an example of "a*b + c" that does not mean "(a*b) + c"...?

[mr.prick]

Show me an example of "a*b + c" that does not mean "(a*b) + c"...?

"({SAE.LONGFT1}+{SAE.LONGFT2})/2"
"({SAE.LONGFT1}+{SAE.LONGFT2}/2)"


How about "(a+b)/c"?
It might not make a difference with "a*b+c" but (a+b)/c" does.
IMO it's better to get into the habit of using them.
A PID like this:
"({SAE.MAP.kPa})-value({SAE.MAP.kPa},frame()-1)"
would not work without brackets.
I'm no fan of syntax errors
Some of the predefined WBO2 PIDs have them and some don't.

[joecar]

...
A PID like this:
"({SAE.MAP.kPa})-value({SAE.MAP.kPa},frame()-1)"
would not work without brackets.

This works (the one and only bracket pair removed):
"{SAE.MAP.kPa}-value({SAE.MAP.kPa},frame()-1)"

value() and frame() are functions and so ( ) are in their syntax.

[mr.prick]

This works (the one and only bracket pair removed):
"{SAE.MAP.kPa}-value({SAE.MAP.kPa},frame()-1)"
value() and frame() are functions and so ( ) are in their syntax.

Not syntax but improper data, as far as this PID is concerned.
I tried a few different combos with this one until I got it to work right.
It originally was this:
"Value({TP},frame()-1)-{TP}"
(I got it from Paul)

The syntax error reference is not relevant here,
just pointing out that it's annoying when it happens.
Just because it "works" doesn't mean it will be right.


Like I said some of the predefined WBO2 PIDs have them and some do not,
even though the expressions are the same.
Example:
Wide Band AFR 1 - LC-1 {CALC.AFR_LC11}
Expression:
AFR = ({EXT.AD1}*3)+7.35

Wide Band AFR 2 - NGK AFX {CALC.AFR_NGK2}
Expression:
AFR = {EXT.AD2}*1.4+9
is VALID

I showed (a+b)/c can result in differing data but (a*b)+c may not.
Whether or not this results in the data being wrong/right
you will need to try both ways to see.
My 2¢

[joecar]

Not syntax but improper data, as far as this PID is concerned.
I tried a few different combos with this one until I got it to work right.
It originally was this:
"Value({TP},frame()-1)-{TP}"
(I got it from Paul)
...

Hmmmm... What was going wrong...? Which {TP} occurance was giving the wrong value, the first or the last...?

If {X} gives a wrong value that is corrected by ({X}) then that is a bug.

Can you post a log file and a calc_pids.txt for me to look at.

That expression is finding the delta in TP from the previous frame to the current frame, right...?

[joecar]

...
Like I said some of the predefined WBO2 PIDs have them and some do not,
even though the expressions are the same.
Example:
Wide Band AFR 1 - LC-1 {CALC.AFR_LC11}
Expression:
AFR = ({EXT.AD1}*3)+7.35

Wide Band AFR 2 - NGK AFX {CALC.AFR_NGK2}
Expression:
AFR = {EXT.AD2}*1.4+9
is VALID

Both of those work correctly.

I showed (a+b)/c can result in differing data but (a*b)+c may not.

a*b+c takes advantage of default precedence, whereas (a+b)/c requires parentheses.

Whether or not this results in the data being wrong/right
you will need to try both ways to see.
My 2¢

I value your 2¢... I'm trying to see this for myself, I'll run a few experiments, I just need to know how to duplicate this and what to look for.

I work with programming languages and compilers everyday, and when the default precedence is not honoured then this is a MAJOR show stopper.

Oh, please do assume smilies in all my posts... ...I'm pretty easy to discuss things with.

[joecar]

This works (the one and only bracket pair removed):
"{SAE.MAP.kPa}-value({SAE.MAP.kPa},frame()-1)"

value() and frame() are functions and so ( ) are in their syntax.

Not syntax but improper data, as far as this PID is concerned.

It originally was this:
"Value({TP},frame()-1)-{TP}"
(I got it from Paul)

...

value() needs ( ) since that's how it groups its parameter list...

frame() same thing, the parameter list is empty.