.STEP log file issue

Dear pavo ,

Thank you for bringing this to our attention. The next release will have this changed. The values will be reported with full precision.

Best Regards,
Mathias

Dear Mathias,

Thank you, I appreciate. Looking forward an update then.

Best regards,

pavo

Edit 2024-02-19:

Hi,

I can see in 24.0.9 it is fixed.

LTspice 24.0.9 for Windows

Circuit: * test1.net: Test of .step

Start Time: Mon Feb 19 09:41:15 2024

solver = Normal

Maximum thread count: 20

Direct Newton iteration for .op point succeeded.

.step volt=100

.step volt=100.0001

.step volt=100.0002

.step volt=100.0003

.step volt=100.0004

.step volt=100.0005

.step volt=100.0006

.step volt=100.0007

.step volt=100.0008

.step volt=100.0009

tnom = 27

temp = 27

method = modified trap

.step volt=100.001

Measurement: volt2

  step volt

     1 100

     2 100.0001

     3 100.0002

     4 100.0003

     5 100.0004

     6 100.0005

     7 100.0006

     8 100.0007

     9 100.0008

    10 100.0009

    11 100.001

Total

 elapsed time: 0.216 seconds.

Now It can be seen some mess in the lines order, extra blank lines and less report parameters comparing to 17.1.15, but the goal of this fix is reached I’d say. Thank you!

Best regards,

pavo

Dearmborn 

Bringing back the old topic... Since version 24.1.3 running the above netlist gives steps shorter than set. We get 12 steps instead of 11.
We have:

.step param volt 100 100.001 .1m

but we get:

LTspice 24.1.7 for Windows
Circuit: C:\dokumenty\ltspice\test\test1.net
Start Time: Tue Apr 15 15:09:45 2025
Options: numdgt = 15  measdgt = 15
solver = Alternate
Maximum thread count: 20
tnom = 27
temp = 27
method = Gear
Direct Newton iteration for .op point succeeded.
.step volt=100
.step volt=100.000090909091
.step volt=100.000181818182
.step volt=100.000272727273
.step volt=100.000363636364
.step volt=100.000454545455
.step volt=100.000545454545
.step volt=100.000636363636
.step volt=100.000727272727
.step volt=100.000818181818
.step volt=100.000909090909
.step volt=100.001
Total elapsed time: 0.615 seconds.

Files loaded:
C:\dokumenty\ltspice\test\test1.net


Measurement: volt2
  step    volt
     1    100
     2    100.000090909091
     3    100.000181818182
     4    100.000272727273
     5    100.000363636364
     6    100.000454545455
     7    100.000545454545
     8    100.000636363636
     9    100.000727272727
    10    100.000818181818
    11    100.000909090909
    12    100.001

Please, take a look.

pavo

Hi pavo ,

Will take a look. Thanks.

mike

Dear pavo ,

.step is handled completely differently by LTspice 24.1.x. It calculates the number of steps upfront. Your case is interesting, because the difference 100.001 - 100 = 0.001 is not representable in binary floating point. Instead, it is

0.00100000004749745130...

As a result, the program determines that one more step is needed. There isn't really a universal solution to this problem of limited machine precision.

I'll have a look, there a are certainly ways to improve this.

Best Regards,
Mathias

Dear mborn 

Ok, then no big issue if we know the root cause. Hope will be somehow improved. Thank you.

Best regards,
pavo

--------------------------
Update 2025-09-10

Hi

It looks like in 24.1.10 it is improved:

.step volt=100
.step volt=100.0001
.step volt=100.0002
.step volt=100.0003
.step volt=100.0004
.step volt=100.0005
.step volt=100.0006
.step volt=100.0007
.step volt=100.0008
.step volt=100.0009
.step volt=100.001
.step volt=100.001 

Only the last step is unnecessarily repeated but it's a minor issue.

LTspice 24.1.10 for Windows
Circuit: C:\dokumenty\ltspice\test\test1.net
Start Time: Wed Sep 10 12:03:25 2025
Options: numdgt = 15  measdgt = 15
solver = Alternate
Maximum thread count: 20
tnom = 27
temp = 27
method = Gear
Direct Newton iteration for .op point succeeded.
.step volt=100
.step volt=100.0001
.step volt=100.0002
.step volt=100.0003
.step volt=100.0004
.step volt=100.0005
.step volt=100.0006
.step volt=100.0007
.step volt=100.0008
.step volt=100.0009
.step volt=100.001
.step volt=100.001
Total elapsed time: 0.624 seconds.

Files loaded:
C:\dokumenty\ltspice\test\test1.net


Measurement: volt2
  step	volt
     1	100
     2	100.0001
     3	100.0002
     4	100.0003
     5	100.0004
     6	100.0005
     7	100.0006
     8	100.0007
     9	100.0008
    10	100.0009
    11	100.001
    12	100.001