/// <summary>No null checks.</summary>
/// <param name="t">Source tensor (can be R1).</param>
/// <param name="newSup">Copy's new superior.</param>
/// <param name="inx">Copy's index inside new superior.</param>
/// <param name="xCap">Extra capacity of all copied (sub)tensors (beyond existing Count).</param>
/// <typeparam name="τ">Numeric type.</typeparam>
/// <typeparam name="α">Arithmetic type.</typeparam>
internal static Tnr <τ, α> CopyAsSubTnrβ <τ, α>(this Tnr <τ, α> t, Tnr <τ, α> newSup,
int inx, int xCap = 0) where τ : notnull, IEquatable <τ>, IComparable <τ> where α : IAlgebra <τ>, new()
{
Assume.True(t.Dim == newSup.Strc[newSup.StrcInx + 1], ()
=> "Source tensor's dimension does not equal the dimension of slot where copied subtensor will be placed.");
if (t is Vec <τ, α> v)
{
return(v.CopyAsSubVecβ(newSup, inx, xCap));
}
else
{
var nst = newSup.SubTnr <τ, α>(inx, t.Count + xCap);
if (t.Rank == 2)
{
foreach (var(i, st) in t)
{
var sv = (Vec <τ, α>)st;
sv.CopyAsSubVecβ <τ, α>(nst, i, xCap);
}
}
else
{
foreach (var(i, st) in t)
{
st.CopyAsSubTnrβ(nst, i, xCap);
}
}
return(nst);
}
}
public void SetT(Tnr <τ, α>?t, params int[] inxs)
{
Tnr <τ, α>?tnr = this;
if (t != null)
{
int n = inxs.Length - 1;
for (int i = 0; i < n; ++i)
{
if (!tnr.TryGetValue(inxs[i], out tnr)) // Crucial line: out tnr becomes the subtensor if found, if not it is created.
{
tnr = new Tnr <τ, α>(tnr !, 6); //new Tensor<τ,α>(Structure, tnr!.Rank - 1, tnr, 6);
tnr.Superior !.AddSubTnr(inxs[i], tnr);
}
}
var dict = (TnrBase <Tnr <τ, α> >)tnr; // tnr is now the proper subtensor.
t.Superior = tnr; // Crucial: to make the added tensor truly a part of this tensor, we must set proper superior and structure.
t.Strc = Strc;
dict[inxs[n]] = t;
}
else
{
for (int i = 0; i < inxs.Length; ++i)
{
if (!tnr.TryGetValue(inxs[i], out tnr)) // t is null and the corresponding substructure does not exist. Leave as is.
{
return;
}
}
tnr.Superior !.Remove(inxs[inxs.Length - 1]);
} // Corresponding tensor exists. Remove.
}
/// <summary>Tensor product of a vector with another tensor. Returns top tensor (null superior) as result.</summary>
/// <param name="t2">Right hand operand.</param>
/// <remarks> <see cref="TestRefs.TensorProduct"/> </remarks>
public static Tnr <τ, α>?TnrProdTop <τ, α>(this Vec <τ, α>?v1, Tnr <τ, α>?t2) where τ : notnull, IEquatable <τ>, IComparable <τ> where α : IAlgebra <τ>, new()
{
if (v1 == null || t2 == null)
{
return(null);
}
return(v1.TnrProdTopß(t2));
}
/// <summary>No null checks.</summary>
/// <param name="sup">Direct superior.</param>
/// <param name="inx">Index inside superior.</param>
/// <param name="cap">Initial capacity.</param>
/// <typeparam name="τ">Numeric type.</typeparam>
/// <typeparam name="α">Arithmetic type.</typeparam>
internal static Vec <τ, α> SubVecβ <τ, α>(this Tnr <τ, α> sup, int inx, int cap = 6) where τ : notnull, IEquatable <τ>, IComparable <τ> where α : IAlgebra <τ>, new()
{
Assume.True(sup.Rank == 2, ()
=> "Vector's superior rank not 2. You can only create a subvec with a rank 2 superior.");
var vec = new Vec <τ, α>(sup, cap);
sup[Vec <τ, α> .V, inx] = vec;
return(vec);
}
/// <summary>Vector getting/setting indexer. Use tnr[1f, 3] = null to remove an entry, should it exist.</summary>
/// <param name="overloadDummy">Type float of first dummy argument specifies that we know we will be getting/setting a Vector.</param>
/// <param name="inxs">A set of indices specifiying which Vector we want to set/get. The set length must reach exactly to Vector rank.</param>
/// <remarks> <see cref="TestRefs.TensorVectorIndexer"/> </remarks>
public Vec <τ, α>?this[Vec <τ, α> overloadDummy, params int[] inx] {
get {
Tnr <τ, α>?tnr = this;
int n = inx.Length - 1;
for (int i = 0; i < n; ++i)
{
if (!tnr.TryGetValue(inx[i], out tnr))
{
return(null);
}
}
if (tnr.TryGetValue(inx[n], out tnr)) // No problem with null.
{
return((Vec <τ, α>)tnr); // Same.
}
else
{
return(null);
}
}
set {
Tnr <τ, α>?tnr = this;
if (value != null)
{
int n = inx.Length - 1; // Entry one before last chooses tensor, last chooses vector.
for (int i = 0; i < n; ++i)
{
if (tnr.TryGetValue(inx[i], out Tnr <τ, α>?tnr2))
{
tnr = tnr2;
}
else // Tensor does not exist in an intermediate rank.
{
tnr = new Tnr <τ, α>(tnr, 4); //new Tensor<τ,α>(Structure, tnr.Rank - 1, tnr, 4);
tnr.Superior !.Add(inx[i], tnr);
}
}
var dict = (TnrBase <Tnr <τ, α> >)tnr; // Tnr now refers to either a prexisting R2 tensor or a freshly created one.
value.Superior = tnr; // Crucial: to make the added vector truly a part of this tensor, we must set proper superior and structure.
value.Strc = Strc;
dict[inx[n]] = value;
} // We do not check that the value is a vector beforehand. It is assumed that the user used indexer correctly.
else
{
int n = inx.Length; // Last entry chooses vector.
for (int i = 0; i < n; ++i)
{
if (!tnr.TryGetValue(inx[i], out tnr))
{
return;
}
}
tnr.Superior !.Remove(inx[n - 1]);
}
} // Vector.Superior.Remove
}
public static Tnr <τ, α>?ContractTopPart2 <τ, α>(this Vec <τ, α> v1, Tnr <τ, α> t2, int rankInx2, List <int> strc, int conDim) where τ : notnull, IEquatable <τ>, IComparable <τ> where α : IAlgebra <τ>, new()
{
if (t2.Rank > 2) // Result is tensor.
{
Tnr <τ, α>?elimTnr2, sumand;
var sum = TopTnr <τ, α>(strc); // Set sum to a zero tensor.
for (int i = 0; i < conDim; ++i)
{
elimTnr2 = t2.ReduceRankTop(rankInx2, i);
if (v1.Scals.TryGetValue(i, out var s) && elimTnr2 != null)
{
sumand = elimTnr2.MulTopβ(s);
sum.SumIntoβ(sumand);
}
}
if (sum.Count != 0)
{
return(sum);
}
else
{
return(null);
}
}
else if (t2.Rank == 2)
{
Tnr <τ, α>?elimTnr2;
Vec <τ, α>?elimVec2, sumand;
var sum = TopVec <τ, α>(strc[0]);
for (int i = 0; i < conDim; ++i)
{
elimTnr2 = t2.ReduceRankTop(rankInx2, i);
if (elimTnr2 != null)
{
elimVec2 = (Vec <τ, α>?)t2.ReduceRankTop(rankInx2, i);
if (v1.Scals.TryGetValue(i, out var s) && elimVec2 != null)
{
sumand = elimVec2.MulTopß(s);
sum.SumIntoß(sumand);
}
}
}
if (sum.Count != 0)
{
return(sum);
}
else
{
return(null);
}
}
else // Result is scalar.
{
throw new ArgumentException("Explicitly cast t2 to vector before using contract.");
}
}
/// <summary>Copies substructure from specified tensor directly into Structure.</summary>
/// <param name="tnr">Source.</param>
protected void AssignStructFromSubStruct(Tnr <τ, α> tnr) // FIXME: Remove this after the copy specs fixes.
{
Strc.Clear();
var subStruct = tnr.Strc.Skip(tnr.StrcInx);
foreach (var emt in subStruct)
{
Strc.Add(emt);
}
}
public Tnr <τ, α> GetNonNullTnr(params int[] inxs)
{
Tnr <τ, α>?tnr = this;
for (int i = 0; i < inxs.Length; ++i)
{
if (!tnr.TryGetValue(inxs[i], out tnr))
{
throw new NullReferenceException("Expected a non-null tensor at specified location.");
}
}
return(tnr);
}
public Tnr <τ, α>?GetT(params int[] inxs)
{
Tnr <τ, α>?tnr = this;
for (int i = 0; i < inxs.Length; ++i)
{
if (!tnr.TryGetValue(inxs[i], out tnr))
{
return(null);
}
}
return(tnr);
}
internal void SetSubTnr(int inx, Tnr <τ, α>?tnr)
{
if (tnr != null)
{
base[inx] = tnr;
tnr.Superior = this;
tnr.Strc = Strc;
}
else
{
Remove(inx);
}
}
/// <summary>No null checks.</summary>
/// <param name="v">Copy source.</param>
/// <param name="newSup">The copied vector's superior.</param>
/// <param name="inx">New index inside superior.</param>
/// <param name="xCap">Extra capacity of copied vector (beyond the number of elements).</param>
/// <typeparam name="τ">Numeric type.</typeparam>
/// <typeparam name="α">Arithmetic type.</typeparam>
internal static Vec <τ, α> CopyAsSubVecβ <τ, α>(this Vec <τ, α> v, Tnr <τ, α> newSup,
int inx, int xCap = 0) where τ : notnull, IEquatable <τ>, IComparable <τ> where α : IAlgebra <τ>, new()
{
Assume.True(v.Dim == newSup.Strc[newSup.StrcInx + 1], ()
=> "Source vector's dimension does not equal the dimension of slot where copied subvector will be placed.");
var copy = SubVec <τ, α>(newSup, inx, v.Count + xCap); // New superior's rank will be checked here.
foreach (var(i, s) in v.Scals)
{
copy.Add(i, s);
}
return(copy);
}
public static Vec <τ, α>?MulSub <τ, α>(this Vec <τ, α>?vec, τ scal, Tnr <τ, α> sup, int inx) where τ : notnull, IEquatable <τ>, IComparable <τ> where α : IAlgebra <τ>, new()
{
α alg = new α();
if (vec == null || alg.IsZero(scal))
{
return(null);
}
else
{
return(vec.MulSubß(scal, sup, inx));
}
}
/// <summary>No null checks.</summary>
/// <param name="sup">Direct superior.</param>
/// <param name="inx">Index inside superior.</param>
/// <param name="cap">Capacity of internal dictionary.</param>
/// <typeparam name="τ">Numeric type.</typeparam>
/// <typeparam name="α">Arithmetic type.</typeparam>
internal static Tnr <τ, α> SubTnrβ <τ, α>(this Tnr <τ, α> sup, int inx, int cap = 6) where τ : notnull, IEquatable <τ>, IComparable <τ> where α : IAlgebra <τ>, new()
{
Assume.True(sup.Rank > 1, ()
=> "Superior's rank too low. Cannot create a subtensor on a vector.");
if (sup.Rank > 2)
{
var tnr = new Tnr <τ, α>(sup, cap);
sup[Tnr <τ, α> .T, inx] = tnr;
return(tnr);
}
else
{
return(sup.SubVecβ(inx, cap));
}
}
/// <summary>No null checks.</summary>
/// <param name="t">Source tensor (can be R1).</param>
/// <param name="xCap">Extra capacity of all copied (sub)tensors (beyond existing Count).</param>
/// <typeparam name="τ">Numeric type.</typeparam>
/// <typeparam name="α">Arithmetic type.</typeparam>
internal static Tnr <τ, α> CopyAsTopTnrβ <τ, α>(this Tnr <τ, α> t, int xCap = 0) where τ : notnull, IEquatable <τ>, IComparable <τ> where α : IAlgebra <τ>, new()
{
if (t is Vec <τ, α> v)
{
return(v.CopyAsTopVecβ(xCap));
}
else
{
var newStrc = t.Substrc;
var copy = TopTnr <τ, α>(newStrc, t.Count + xCap);
foreach (var(i, st) in t)
{
st.CopyAsSubTnrβ <τ, α>(copy, i, xCap);
}
return(copy);
}
}
/// <summary>Tensor getting/setting indexer.</summary>
/// <param name="overloadDummy">Type uint of first dummy argument specifies that we know we will be getting/setting a Tensor.</param>
/// <param name="inxs">A set of indices specifiying which Tensor we want to set/get. The set length must not reach all the way out to scalar rank.</param>
public Tnr <τ, α>?this[Tnr <τ, α> overloadDummy, params int[] inxs] {
get {
Tnr <τ, α>?tnr = this;
for (int i = 0; i < inxs.Length; ++i)
{
if (!tnr.TryGetValue(inxs[i], out tnr))
{
return(null);
}
}
return(tnr);
} // No problem with tnr being null. We return above.
set {
Tnr <τ, α>?tnr = this;
if (value != null)
{
int n = inxs.Length - 1;
for (int i = 0; i < n; ++i)
{
if (!tnr.TryGetValue(inxs[i], out tnr)) // Crucial line: out tnr becomes the subtensor if found, if not it is created
{
tnr = new Tnr <τ, α>(tnr !, 6); //new Tensor<τ,α>(Structure, tnr!.Rank - 1, tnr, 6);
tnr.Superior !.AddSubTnr(inxs[i], tnr);
}
}
var dict = (TnrBase <Tnr <τ, α> >)tnr; // tnr is now the proper subtensor.
value.Superior = tnr; // Crucial: to make the added tensor truly a part of this tensor, we must set proper superior and structure.
value.Strc = Strc;
dict[inxs[n]] = value;
}
else
{
for (int i = 0; i < inxs.Length; ++i)
{
if (!tnr.TryGetValue(inxs[i], out tnr))
{
return;
}
}
tnr.Superior !.Remove(inxs[inxs.Length - 1]);
}
}
}
/// <summary>Creates a top tensor from an array span.</summary>
/// <param name="span">Array span of values.</param>
/// <param name="strc">Structure.</param>
/// <typeparam name="τ">Numeric type.</typeparam>
/// <typeparam name="α">Arithmetic type.</typeparam>
public static Tnr <τ, α>?TopTnrFromSpan <τ, α>(Span <τ> span, params int[] strc) where τ : notnull, IEquatable <τ>, IComparable <τ> where α : IAlgebra <τ>, new()
{
int rank = strc.Length;
if (rank == 1)
{
return(TopVecFromSpan <τ, α>(span));
}
else
{
var res = new Tnr <τ, α>(strc.ToList(), strc[0]); // Empty tensor that enters recursion.
Recursion(span, 0, res);
return(res.Count != 0 ? res : null);
}
void Recursion(Span <τ> spn, int slot, Tnr <τ, α> tgt) // Span and natural slot index to which it belongs.
{
int nIter = strc[slot]; // As many iterations as slot dimension.
int nEmtsInSpan = spn.Length / nIter;
if (tgt.Rank > 2)
{
for (int i = 0; i < nIter; ++i) // Over each tensor. Create new spans and run recursion on them.
{
var newSpn = spn.Slice(i * nEmtsInSpan, nEmtsInSpan);
var subTnr = new Tnr <τ, α>(tgt, strc[slot]);
Recursion(newSpn, slot + 1, subTnr);
if (subTnr.Count != 0)
{
tgt.Add(i, subTnr);
}
}
}
else // We are at rank 2, subrank = vector rank.
{
for (int i = 0; i < nIter; ++i)
{
var newSlc = spn.Slice(i * nEmtsInSpan, nEmtsInSpan);
var subVec = SubVecFromSpan <τ, α>(newSlc, tgt, i);
}
}
}
}
public Vec <τ, α> GetNonNullVec(params int[] inx)
{
Tnr <τ, α>?tnr = this;
int n = inx.Length - 1;
for (int i = 0; i < n; ++i)
{
if (!tnr.TryGetValue(inx[i], out tnr))
{
throw new NullReferenceException("Expected a non-null tensor at specified location.");
}
}
if (tnr.TryGetValue(inx[n], out tnr))
{
return((Vec <τ, α>)tnr);
}
else
{
throw new NullReferenceException("Expected a non-null vector at specified location.");
};
}
public Vec <τ, α>?GetV(params int[] inx)
{
Tnr <τ, α>?tnr = this;
int n = inx.Length - 1;
for (int i = 0; i < n; ++i)
{
if (!tnr.TryGetValue(inx[i], out tnr))
{
return(null);
}
}
if (tnr.TryGetValue(inx[n], out tnr)) // No problem with null.
{
return((Vec <τ, α>)tnr); // Same.
}
else
{
return(null);
}
}
internal static Tnr <τ, α> TnrProdTopß <τ, α>(this Vec <τ, α> v1, Tnr <τ, α> t2) where τ : notnull, IEquatable <τ>, IComparable <τ> where α : IAlgebra <τ>, new()
{
if (t2.Rank > 1)
{
int newRank = v1.Rank + t2.Rank;
var strc1 = v1.EnumSubstrc();
var strc2 = t2.EnumSubstrc();
var newStrc = strc1.Concat(strc2).ToList();
// We must substitute this vector with a tensor whose elements are multiples of tnr2.
var prod = TopTnr <τ, α>(newStrc, v1.Scals.Count);
foreach (var(i, s1) in v1.Scals)
{
t2.MulSubβ(s1, prod, i);
}
return(prod);
}
else
{
var v2 = (Vec <τ, α>)t2;
return(v1.TnrProdTopß(v2));
}
}
/// <summary>Creates a non-top vector from an array span. Adds it to its specified superior at the specified index.</summary>
/// <param name="span">Array span of values.</param>
/// <param name="sup">Direct superior with an existing structure.</param>
/// <param name="inx">Index inside superior.</param>
/// <typeparam name="τ">Numeric type.</typeparam>
/// <typeparam name="α">Arithmetic type.</typeparam>
public static Vec <τ, α>?SubVecFromSpan <τ, α>(Span <τ> span, Tnr <τ, α> sup, int inx) where τ : notnull, IEquatable <τ>, IComparable <τ> where α : IAlgebra <τ>, new()
{
Assume.True(sup.Rank == 2, () => "Vector's superior rank not 2. You can only create a subvector with a rank 2 superior.");
α alg = new α();
var vec = new Vec <τ, α>(sup, span.Length);
for (int i = 0; i < span.Length; ++i)
{
if (!alg.IsZero(span[i]))
{
vec.Add(i, span[i]);
}
}
if (vec.Count > 0) // Created vector is not empty.
{
sup[Vec <τ, α> .V, inx] = vec;
return(vec);
}
else
{
return(null);
}
}
/// <summary>Compares substructures and values.</summary> /// <param name="tnr2">Tensor to compare to.</param> public bool Equals(Tnr <τ, α>?tnr2) => this.Equalsβ <τ, α>(tnr2);
[MaybeNull] // Getter may return null.
public virtual τ this[params int[] inx] {
get {
α alg = new α();
Tnr <τ, α>?tnr = this;
int n = inx.Length - 2;
for (int i = 0; i < n; ++i)
{
if (!tnr.TryGetValue(inx[i], out tnr))
{
return(alg.Zero);
}
}
if (tnr.TryGetValue(inx[n], out tnr)) // No probelm with null.
{
var vec = (Vec <τ, α>)tnr; // Same.
if (vec.Scals.TryGetValue(inx[n + 1], out τ val))
{
return(val);
}
}
α alg2 = new α();
return(alg.Zero);
}
set {
Tnr <τ, α>?tnr = this;
Tnr <τ, α>?tnr2; // Temporary to avoid null problem below.
Vec <τ, α> vec;
α alg = new α();
if (!alg.IsZero(value))
{
if (inx.Length > 1) // At least a 2nd rank tensor.
{
int n = inx.Length - 2;
for (int i = 0; i < n; ++i) // This loop is entered only for a 3rd rank tensor or above.
{
if (tnr.TryGetValue(inx[i], out tnr2))
{
tnr = tnr2;
}
else
{
tnr = new Tnr <τ, α>(tnr, 6); //new Tensor<τ,α>(Structure, tnr.Rank - 1, tnr, 6);
tnr.Superior !.Add(inx[i], tnr);
}
}
if (tnr.TryGetValue(inx[n], out tnr2)) // Does vector exist?
{
vec = (Vec <τ, α>)tnr2;
}
else
{
vec = new Vec <τ, α>(Strc, tnr, 4);
tnr.Add(inx[n], vec);
}
vec.Scals[inx[n + 1]] = value;
}
}
else
{
int n = inx.Length - 1;
for (int i = 0; i < n; ++i)
{
if (!tnr.TryGetValue(inx[i], out tnr))
{
return;
}
}
vec = (Vec <τ, α>)tnr;
vec.Scals.Remove(inx[n]);
}
}
}
internal static Vec <τ, α> MulSubß <τ, α>(this Vec <τ, α> vec, [DisallowNull] τ scal, Tnr <τ, α> sup, int inx) where τ : notnull, IEquatable <τ>, IComparable <τ> where α : IAlgebra <τ>, new()
{
α alg = new α();
var newVec = TnrFactory.SubVec <τ, α>(sup, inx);
foreach (var(i, s) in vec)
{
newVec.Add(i, alg.Mul(scal, s) !); // Return of Mul is not null zero (if both inputs were not zero):
}
return(newVec);
}
/// <summary>Creates a deep copy of a tensor as a non-top tensor (non-null superior).</summary>
/// <param name="t">Copy source.</param>
/// <param name="newSup">The copied tensor's superior.</param>
/// <param name="inx">New index inside superior.</param>
/// <param name="xCap">Extra capacity of all copied (sub)tensors (beyond existing Count).</param>
/// <typeparam name="τ">Numeric type.</typeparam>
/// <typeparam name="α">Arithmetic type.</typeparam>
public static Tnr <τ, α>?CopyAsSubTnr <τ, α>(this Tnr <τ, α>?t, Tnr <τ, α> newSup,
int inx, int xCap = 0) where τ : notnull, IEquatable <τ>, IComparable <τ> where α : IAlgebra <τ>, new()
=> t != null?t.CopyAsSubTnrβ(newSup, inx, xCap) : null;
/// <summary>Creates a non-top vector (non-null superior) with specified initial capacity. Adds it to its specified superior at the specified index. Dimension is inferred from superior's structure.</summary> /// <param name="sup">Direct superior.</param> /// <param name="inx">Index inside superior.</param> /// <param name="cap">Initial capacity.</param> /// <typeparam name="τ">Numeric type.</typeparam> /// <typeparam name="α">Arithmetic type.</typeparam> public static Vec <τ, α> SubVec <τ, α>(this Tnr <τ, α>?sup, int inx, int cap = 6) where τ : notnull, IEquatable <τ>, IComparable <τ> where α : IAlgebra <τ>, new() => sup != null?SubVecβ(sup, inx, cap) : throw new ArgumentNullException(nameof(sup), "Specified superior was null.");
public static Tnr <τ, α>?ContractTop <τ, α>(this Vec <τ, α> v1, Tnr <τ, α> t2, int slot2) where τ : notnull, IEquatable <τ>, IComparable <τ> where α : IAlgebra <τ>, new()
{
(List <int> strc, _, int rankInx2, int conDim) = v1.ContractTopPart1(t2, 1, slot2);
return(ContractTopPart2(v1, t2, rankInx2, strc, conDim));
}
/// <summary>Creates a deep copy of a tensor as a top tensor (null superior).</summary> /// <param name="t">Source tensor (can be R1).</param> /// <param name="xCap">Extra capacity of all copied (sub)tensors (beyond existing Count).</param> /// <typeparam name="τ">Numeric type.</typeparam> /// <typeparam name="α">Arithmetic type.</typeparam> public static Tnr <τ, α>?CopyAsTopTnr <τ, α>(this Tnr <τ, α>?t, int xCap = 0) where τ : notnull, IEquatable <τ>, IComparable <τ> where α : IAlgebra <τ>, new() => t != null?t.CopyAsTopTnrβ(xCap) : null;
/// <summary>Constructor with redundancy, used internally.</summary>
/// <param name="strc">Structure (absorbed).</param>
/// <param name="sup">Direct superior.</param>
/// <param name="cap">Capacity of internal dictionary.</param>
internal Vec(List <int> strc, Tnr <τ, α>?sup, int cap) :
base(strc, 1, sup, 0) // Zero capacity for dictionary holding tensors.
{
Scals = new Dictionary <int, τ>(cap);
}
/// <summary>Creates a deep copy of a vector as a non-top vector (non-null superior).</summary>
/// <param name="v">Copy source.</param>
/// <param name="newSup">The copied vector's superior.</param>
/// <param name="inx">New index inside superior.</param>
/// <param name="xCap">Extra capacity of copied vector (beyond the number of elements).</param>
/// <typeparam name="τ">Numeric type.</typeparam>
/// <typeparam name="α">Arithmetic type.</typeparam>
public static Vec <τ, α>?CopyAsSubVec <τ, α>(this Vec <τ, α>?v, Tnr <τ, α> newSup,
int inx, int xCap = 0) where τ : notnull, IEquatable <τ>, IComparable <τ> where α : IAlgebra <τ>, new()
=> v != null?v.CopyAsSubVecβ(newSup, inx, xCap) : null;
/// <summary>Creates a non-top vector with specified superior and initial capacity. Does not add the new vector to its superior or check whether the superior is rank 2.</summary>
/// <param name="sup">Direct superior.</param>
/// <param name="cap">Capacity of internal dictionary.</param>
internal Vec(Tnr <τ, α> sup, int cap) : this(sup.Strc, sup, cap)
{
}
