fix vector_arrowsize

Author: ytdHuang

docs/src/users_guide/plotting_the_bloch_sphere.md

@@ -195,7 +195,7 @@ At the end of the last section we saw that the colors and marker shapes of the d
 | `b.sphere_alpha` | Transparency of sphere surface | `"#FFDDDD"` |
 | `b.vector_color` | Colors for vectors | `["green", "#CC6600", "blue", "red"]` |
 | `b.vector_width` | Width of vectors | `0.025` |
-| `b.vector_arrowsize` | Arrow size parameters as `[head_length, head_width, stem_width]` | `[0.07, 0.08, 0.08]` |
+| `b.vector_arrowsize` | Scales the size of the arrow head. The first two elements scale the radius (in `x/y` direction) and the last one is the length of the cone. | `[0.07, 0.08, 0.08]` |
 | `b.view` | Azimuthal and elevation viewing angles in degrees | `[30, 30]` |
 | `b.xlabel` | Labels for x-axis | `[L"x", ""]` (``+x`` and ``-x``) |
 | `b.xlpos` | Positions of x-axis labels | `[1.2, -1.2]` |

ext/QuantumToolboxMakieExt.jl

@@ -661,9 +661,15 @@ Scales vectors appropriately and adds `3D` arrow markers.
 """
 function _plot_vectors!(b::Bloch, lscene)
     isempty(b.vectors) && return nothing
+
+    arrow_head_length = b.vector_arrowsize[3]
     for (i, v) in enumerate(b.vectors)
         color = get(b.vector_color, i, RGBAf(0.2, 0.5, 0.8, 0.9))
-        vec = 0.92 * Vec3f(v...) # multiply by 0.92 so that the point edge of the arrow represents the actual position
+        nv = norm(v)
+        (arrow_head_length < nv) || throw(ArgumentError("The length of vector arrow head (Bloch.vector_arrowsize[3]=$arrow_head_length) should be shorter than vector norm: $nv"))
+
+        # multiply by the following factor makes the end point of arrow head represent the actual vector position.
+        vec = (1 - arrow_head_length / nv) * Vec3f(v...)
         arrows!(
             lscene,
             [Point3f(0, 0, 0)],

src/visualization.jl

@@ -102,7 +102,7 @@ A structure representing a Bloch sphere visualization for quantum states. Availa
 
 - `vector_color::Vector{String}`: Colors for vectors
 - `vector_width::Float64`: Width of vectors
-- `vector_arrowsize::Vector{Float64}`: Arrow size parameters as `[head_length, head_width, stem_width]`
+- `vector_arrowsize::Vector{Float64}`: Scales the size of the arrow head. The first two elements scale the radius (in `x/y` direction) and the last one is the length of the cone.
 
 ## Layout properties