## If a description in D&D 5e is lacking, is it valid to refer to an older edition?

In 5e, Tenser’s Floating Disc

follows you so that it stays within 20’ of you.
(5e PHB282)

The spell description does not make mention of its travel rate, but in 3.5e the description says:

It floats along horizontally within spell range and will accompany you at a rate of no more than your normal speed each round. (3.5e PHB294)

Could the lack of follow speed in 5e be extrapolated from the description in 3.5e?

## Is an Immovable Rod a valid spellcasting focus? [duplicate]

The Dungeon Master’s Guide classifies an immovable rod as a rod rather than a wondrous item. Does this imply that it is a valid spellcasting focus? If not, what purpose does this classification serve?

## What happens to a Chain lighting with invalid primary target and valid secondary targets?

This question asks what happens when a single-target spell has an invalid target. (A target that is not legitimately permissible, not a target that is weak from illness or injury).

The answer appears to be: that depends on whether one wishes to implement an older Sage Advice segment of a Dragon Talk podcast, or the more recent but optional written rules in Xanathar’s Guide to Everything.

Assume for this question that I prefer XGtE.

The rule for resolving invalid spell targets states (XGtE 85-86):

If you cast a spell on someone or something that can’t be affected by the spell, nothing happens to that target, but if you used a spell slot to cast the spell, the slot is still expended.

Now consider the chain lightning spell, in which

You create a bolt of lightning that arcs toward a target of your choice that you can see within range. Three bolts then leap from that target to as many as three other targets, each of which must be within 30 feet of the first target. A target can be a creature or an object and can be targeted by only one of the bolts.

Suppose my primary target for the spell is invalid, because it is not a creature or an object. If an example must be given, suppose it is an illusion. However, each of the three secondary targets of the spell are valid, being either creatures or objects.

Do I spend the spell slot with nothing happening at all, or does the slot get spent, the chain lightning impact the illusion but do nothing to it and then leap to the three valid targets with the full effects given in the spell description?

Note: I am assuming that an illusion is not an object, based largely on my interpretation that an illusion is not an "item" and on the text of the 14th-level School of Illusion wizard feature, Illusory Reality. I am open to frame challenges that demonstrate that illusions are, in fact, objects, but such answers will be better if they then either provide a more appropriate example of something that is not a creature or an object, or demonstrate that the question is moot since everything is at least either a creature or an object.

## Can blank target and range spells be considered valid for the teamwork feat share spells?

In a past question I asked if there was a way to cast personal spells on other creatures, and a solution was given. It requires the teamwork feats bonded mind and shared spells, further enhanced by the spell Coordinated Effort.

So the hard part was finished or so I thought. I was expecting a plethora of wonderful buff spells that are mediocre or situational to a caster, but a wonderful boon to martial and others. Searching d20 with "Target You" and "Range personal". This was further complicated by the fact that not all spells have the right information. Take Bless and Detect Evil which both are missing range and target. Are these valid spells?

So the question is, spells whose description include you/the caster and without range/target allowed?

There is a similar question I asked but was specifically about the normal familiar share spells ability.

## What type of targets are valid for Scorching Ray?

Almost all the attack spells in the PHB specific the type of target as either a creature, an object, or a point in space (as per Target section on PHB pg 204).

Scorching Ray just says

You create three rays of fire and hurl them at targets within range

But it doesn’t specify what types of targets (creature, object, point in space). Should I interpret that to mean all three are then valid? I couldn’t find anything in the Errata or Sage Advice Compendium on this specifically.

## What does it mean by the error “10 is not a valid variable”?

I wrote a very basic test function in Mathematica (I am the absolute beginner)

Fun1[x_] := Module[ {y, z, t}, y = Min[x + 10000, 500]; z = y + 24; t = y + z; t ] 

However, when I try to solve for the root Solve[Fun1[x] == 0, x], I was never able to get the expected value, but this error occurred "… Solve::ivar: 10 is not a valid variable".

what does it mean? and how to overcome this?

Many thanks Tien

## call_user_func() expects parameter 1 to be a valid callback … => brak możliwości zalogowania się do panelu administracyjnego

Warning: call_user_func() expects parameter 1 to be a valid callback, first array member is not a valid class name or object in /wordpress/wp-content/plugins/cache-enabler/inc/cache_enabler.class.php on line 1752

## Long after the demise of Google Authorship, is it now both valid and viable for a document to include multiple links?

When Google Authorship was very much still a thing several years ago, the conclusion was that it was better not to include more than one <link rel="author"> on any given page.

See:

• 2012 – How to implement rel="author" on a page with multiple authors?

Google Authorship is now a distant memory (Mountain View stopped using it several centuries ago in 2016) but I’m concerned that there may still be something invalid or nonsensical about including more than one <link rel="author"> in the <head> of a given document.

My use case involves referencing both an About Page and humans.txt:

<link rel="author" href="https://example.com/about-us/" /> <link rel="author" href="https://example.com/humans.txt" type="text/plain" /> 

Is there anything – I can’t find explicit confirmation – from the WHAT-WG to confirm that this is valid usage?

Or is there a viable alternative to using more than one <link rel="author"> element?

## Finding a valid equation for fixed point problem

I currently am working on learning more about fixed point method. Finding equations that satisfy the constraints of a g function can sometimes require a bit of engineering. I have come across one that many would consider simple. Yet, I have been stuck on it for some time now.

Here it is $$f(x) = x^2 – x – 2 = 0$$ on $$[1.5,3]$$.

I have tried many things; however, I have yet to successfully discover one that maps domain to range for both $$g$$ and $$g^\prime$$.

Would anyone be able to give me a guiding hand?

## Find the maximum number of valid cartesian coordinates

Given a list X containing m number of x coordinates and a list Y containing m number of y coordinates. The coordinate (x, y) is valid if and only if the difference between x and y is less than or equal to d. I need to find out the maximum number of valid coordinates. Here is my algorithm.

sort the list X in non-decreasing order sort the list Y in non-decreasing order for x in X:      for y in Y:          if abs(x - y) <= d:              let x match with y              remove x from X              remove y from Y 

Can this algorithm give me maximum number of valid pairs? If yes, is there any more efficient algorithm? The nested loop means the worst-case time is $$O(m^2)$$. Is there any log linear time $$O(mlogm)$$ algorithm for this question?