## What effect does learning a spell have for a sorcerer?

I’ve read and reread Learn a Spell several times, and I just don’t understand it.

For a wizard, it makes sense – the wizard adds the spell to their spellbook. But for both of the other options, I don’t understand what effect it has.

From the feat:

If you have a spellbook, Learning a Spell lets you add the spell to your spellbook; if you prepare spells from a list, it’s added to your list; if you have a spell repertoire, you can select it when you add or swap spells.

if you prepare spells from a list

What classes does this apply to? Cleric? Surely if a character prepares spells from a list, then that character has access to the entire tradition’s spell list – what benefit does learning a spell have for a class like Cleric or Druid?

if you have a spell repertoire, you can select it when you add or swap spells.

For a class like Sorcerer, as I understand it their repertoire can only ever contain as many spells as the number of spell slots they have.

So let’s say at level 1, a draconic sorcerer uses the Learn a Spell activity to learn Fear, a spell in the Arcane tradition. They don’t have Fear in their repertoire already, and they succeed at the check. If I’m right, then can’t use that spell until they level up, or spend downtime swapping another spell in their repertoire out for that spell.

But this doesn’t make sense to me either – the way the spell repertoire feature is phrased, it makes it sound like the sorcerer would be able to swap out one of the spells in their repertoire for any spell of the same level in the Arcane tradition’s spell list (Fear included) anyway when they level up – so what was the point of learning it?

Is there a subset of tradition spells that a sorcerer knows, which is somehow distinct from the sorcerer’s repertoire?

Or is the activity purely intended to allow spontaneous casters to add uncommon-or-rarer spells to their repertoire?

If someone can explain this to me, I’d really appreciate it!

## Guidance on Learning to GM Star Trek Adventures

I have been GMing DnD5e for almost two years now and have two consistent groups ongoing. As a Christmas gift, I will be running a game using the Star Trek Adventures game system for someone.

I have the rulebook, have begun reading it, and suspect that this question will be closed for being too broad: what notable differences from DnD5e should I pay attention to so I can most effectively learn and teach this new system? For your information, only one of my potential players has played a roleplaying game in the last 25 years, as she is in one of my 5e groups.

This question is less about the success/failure system inherent to the roles, but more specifically about how the ‘scenes’ are set up, how the characters are intended to act, and the types of challenges that ought to be presented, but all answers providing important details that I must adapt to are relevant.

Thank you!

## Do Order of the Scribes wizards have reduced spell learning GP costs?

The Player’s Handbook uses the following language to explain how wizards obtain spells:

Copying a Spell into the Book. When you find a wizard spell of 1st level or higher, you can add it to your spellbook if it is of a spell level you can prepare and if you can spare the time to decipher and copy it.

Copying that spell into your spellbook involves reproducing the basic form of the spell, then deciphering the unique system of notation used by the wizard who wrote it. You must practice the spell until you understand the sounds or gestures required, then transcribe it into your spellbook using your own notation.

For each level of the spell, the process takes 2 hours and costs 50 gp. The cost represents material components you expend as you experiment with the spell to master it, as well as the fine inks you need to record it. Once you have spent this time and money, you can prepare the spell just like your other spells.

The "Wizardly Quill" ability in the Unearthed Arcana that first described Order of the Scribes wizards used the following language:

• The quill doesn’t require ink. When you write with it, it produces ink in a color of your choice on the writing surface.

• The gold and time you must spend to copy a spell into your spellbook are halved if you use the quill for the transcription.

In the final release of the class through Tasha’s Cauldron of Everything, the language has changed to the following:

• The quill doesn’t require ink. When you write with it, it produces ink in a color of your choice on the writing surface.

• The time you must spend to copy a spell into your spellbook equals 2 minutes per spell level if you use the quill for the transcription.

There are, it seems, at least two interpretations of how this affects spell learning costs:

1. Wizardly Quill does not say anything about the GP cost of learning spells, and therefore, the costs remain unchanged.
2. Wizardly Quill reduces the cost of ink to 0 GP. Spells cost 50 GP/level when learning spells that require costly material components (e.g. Find Familiar). Spells cost 0 GP/level when learning spells whose material components are substituted by an arcane focus (e.g. Feather Fall).

My inclination, based on the Rule of Specificity, is to rule for the first option.

## does learning the same spell from different sources allow it to benefit from bonuses from all sources?

For example, an Arcana cleric takes Firebolt with Arcane Initiate, then multiclasses with Artillerist artificer, and also takes Firebolt as one of the Artificer cantrips. Assuming this character has 5 levels as an Artillerist and 8 levels in Arcana Domain,

would casting Firebolt through an Arcane Firearm count as both an artificer spell for the Arcane Firearm feature, and a cleric cantrip for the Potent Spellcasting feature?

## Recomendation for material, books in order to learn Machine Learning / Deep learning using Mathematica?

I know that there are plenty of resources web sites and books, MOOC to learn Machine Learning and Deep Learning mostly in Python.

However, I am so curious to know how to learn and code using Mathematica.

Wellcome and thankful for interesting comments about what version it works, libraries, books, tutorials, ebooks, etc for Mathematica users.

## Learning Magic: The Problem

In Advanced Dungeons & Dragons (1st & 2nd editions) the rules required that all ‘magic-users’ have Read Magic as a basic requirement to do any wizarding (so-called in later editions) whatsoever.

Down through the editions this tradition was lost. Moreover, there is not a single spell that: allows a wizard to teach a student, assist fellow wizard in understanding their personal works, nor some magical process whereby a magic-scroll writer might assist a friendly caster to make use of enchanted-scribed works.

With this interpretation of Illusory Script it may be possible to solve these three lore-issues at once. Yet how much is sacrificed in the RAW & RAI for RAF & ‘rules of cools‘. The question:

Can Illusory Script be a heuristic / learning device for the training of one’s first cantrips, the learning of a friendly wizard’s spells and/or assistance on casting a friendly caster’s scroll?

Here we provide both logic for why it might work (and why it would be great role-playing if it did).

### The RAW Spell: Conveys A Specific Meaning That A Caster Intends.

The spell Illusory Script gives any written work two levels or layers of use &/or meaning. The foundation-layer gains this power:

To you and any creatures you designate when you cast the spell, the writing appears normal, written in your hand, and conveys whatever meaning you intended when you wrote the text. To all others, the writing appears as if it were written in an unknown or magical script that is unintelligible. Alternatively, you can cause the writing to appear to be an entirely different Message, written in a different hand and language, though the language must be one you know.(emphasis added by writer)

### What This Means: Uses For Meanings Conveyed

• Spell books are for a purpose or meaning (i.e. ‘how to memorize/prepare spells’). After a long rest a wizard reviews their own written works, then they gain choices to apply on these freshly regained spells (or ‘slots’). Understanding and scribing new spells from another book takes considerable time & effort.

If one could gain this implied intended meaning directly from an original caster, they could learn the spell as if the book were their own. Thus, reading an alien spell book with Illusory Script (and permission-access) renders spells ready for use. Once a spell is in mind (‘memorized’ or ‘prepared’), actual scribing in one’s own book is faster, easier and cheaper (less than half the time & price).

• Casting spells from a magic-scroll of a higher spell-slot has serious risk involved. Given the conveyed meaning listed above may give either: automatic success, advantage – or even some kind of proficiency bonus.

### The underlying mechanics

A 3rd level+ person (from any class) must train up a ‘zero-level’ non-magical peasant-peon to first level ‘apprentice’ stage, i.e. able to use at least one cantrip. Clerics and Druids are inspired via various celestial, fae &/or fiendish sources, miraculously empowered for appropriate supplicants. Sorcerers are just born that way. For bards, wizards and some warlocks such easy pathways are not available. Using a cantrip-scroll written by a 3rd lvl+ bard, wizard or warlock combined with Illusory Script allows the writer-‘master’ to pass on deep magical understandings with intentional meanings – directly into the student. This heuristic allows any apprentice, no matter how thick, to gain their first cantrip… breaking otherwise impossible barriers.

### The Illusion As A Heuristic: Koans & Riddles

• Breaking Down Mental Barriers: An illusory message as a riddle that grants passage to the ‘real’ message is brilliant lore-wise. Imagine: upon a bard’s mastery of a ballad’s score the music sheets reveal Vicious Mockery; upon signing soul-binding documents with blood, the scale lifts, or; the researching apprentice would see through the illusion to find yet another illusion. This re-skinning of Illusory Script transforms this minimally used spell to a pivotal plot point.

• Time pressure for ambitious students: After ten days this spell’s magic fades, leaving the otherwise incomprehensible scribed-spell or magic-scroll behind. Sure the knowledge &/or magic remains but the bridge of understanding is gone. Imagine the frantic apprentice bard, warlock &/or wizard on day nine just feeling the pressure of their search or study.

### Exemplary Precedent: Mind-Altering Illusions

Though the illusion-spells Phantasmal Force, Dream and Weird all modify minds, only Illusory Script specifically conveys a caster’s meaning.

Author’s note: I am looking for a general understanding here. Please don’t answer with ‘I don’t understand the question’ or ‘you answered this yourself!’ or ‘moved to discussion’ or ‘let the DM decide!’ –

Bottom Line: I just want to know if (and why) this would work RAW / RAI.

## Multi-Interval Discretization of Continuous-Valued Attributes for Classification Learning

I’m trying to figure out Fayyad and Irani (1993) MDLP discretization of continuous variables (here is link to the original paper). I understand how algorithm works, but I have some doubts about first step, sorting of variable and finding potential cut-points.

My doubt is what happens if we have multiple occurrence of same value of variable in the dateset and those occurrences have different target variable associated with them? This can happen quite often in practice, e.g. we have table of clients with some properties which is 0 for some large number of them and there are multiple different events associated with those clients, some of them belonging to one class and others belonging to different class.

Here is a dummy table with sorted Variable X and 2-class classification problem:

If we apply heuristic like it is suggested in the paper, value 0.6 will end up in multiple different potential bins since it contains both class 0 and 1. What’s even worst, it seems that potential cutoffs and bins will be different if we sort target variable (ascending, descending or unsorted)…

Any help with this, someone maybe already tried to figure out this?

## Complete proof of PAC learning of axis-aligned rectangles

I have already read PAC learning of axis-aligned rectangles and understand every other part of the example.

From Foundations of Machine Learning by Mohri, 2nd ed., p. 13 (book) or p. 30 (PDF), I am struggling to understand the following sentence of Example 2.4, which is apparently the result of a contrapositive argument:

… if $$R(\text{R}_S) > \epsilon$$, then $$\text{R}_S$$ must miss at least one of the regions $$r_i$$, $$i \in [4]$$.

i.e., $$i = 1, 2, 3, 4$$. Could someone please explain why this is the case?

The way I see it is this: given $$\epsilon > 0$$, if $$R(\text{R}_S) > \epsilon$$, then $$\mathbb{P}_{x \sim D}(\text{R}\setminus \text{R}_S) > \epsilon$$. We also know from this stage of the proof that $$\mathbb{P}_{x \sim D}(\text{R}) > \epsilon$$ as well. Beyond this, I’m not sure how the sentence above is reached.

## In a machine learning system, why use differentially private SGD if our input data is already perturbed by a DP mechanism?

I’m trying to implement my own version of a deep neural network with differential privacy to preserve the privacy of the parties involved in the training dataset.

I’m using the method by Abadi et al. proposed in their seminal paper Deep Learning with Differential Privacy as the basis of my implementation. Now I have trouble understanding one thing in this paper. In their method, they propose a differentially private SGD optimisation function and they use an accountant to keep their privacy budget expenditure during each iteration. All of this makes sense: every time you query the data, you need to add controlled noise to it to mitigate the risk of leakage. But before they begin the training process, they add a differentially private PCA layer and filter their data through it.

My confusion is about why we do need to have DP-SGD after this (or the other way around, why DP-PCA when we’re already ensuring DP with our DP-SDG method). I mean, based on post-processing principle, if a mechanism is say (epsilon)-DP, any function performed on the output of that mechanism is also (epsilon)-DP. Now since we’re already applying an (epsilon)-differentially private PCA mechanism on our data, why do we need to have the whole DP-SGD process after that? I understand the problem with local DP and why it’s much more efficient to do global DP on the model instead of the training data, but I’m wondering if we’re already applying DP during the training phase, is it really necessary for the PCA to be DP as well or could we have just used normal DP or another dimensionality reduction method?

## Learning about Exploitation using VMs. What vulnerabilities should I be implementing? [closed]

Recently, I’ve been working on a project to learn a little bit about the exploitation of vulnerable systems (kind of like vulnhub). Problem is, I want to do it DIY (learn more about configuration / setup this way), but I don’t really know what vulnerabilities to implement on a "victim" Debian machine that I will "attack" with Kali Linux (all in VMs at the moment).

What I’m looking for: Vulnerabilities that are seen commonly in real-world production environments. Misconfigurations or bugs in common programs / operating systems. I want to simulate something realistic — not too vulnerable yet still vulnerable enough to exploit and learn something. That’s not necessarily to say that Remote Code Exec and Priv Esc are unwanted; I just want to limit the number of those kinds of vulns to make my attack paths more interesting.

In other words, what general kinds of exploits or programs (OpenSMTPD, PHP stuff, etc.) that have historically been pretty vulnerable are there that I can install / configure onto my vulnerability lab and play around with? If applicable, a corresponding CVE would be really helpful too. Shoot me with your recommendations.