undo hard disk partition

I was wanting to be able to run both Yosemite and El Capitan on the same machine so test out whether my heritage software was going to work.

http://www.macworld.co.uk/how-to/mac-software/get-el-capitan-on-your-mac-without -losing-your-existing-os-x-install-3623514/

I would really appreciate some help with this.

So far I have stumbled across http://apple.stackexchange.com/questions/144010/cant-create-partition-on-free-sp ace-with-disk-utility which suggests trying the following

1) Open Terminal.

2) Enter the following command to find the UUID of the Logical Volume. Make sure you select the correct UUID. Copy it.

diskutil cs list

3) Enter the following command (replacing lvUUID with the copied lvUUID) to resize the logical volume back to it's full capacity. Enter your password when prompted.

sudo diskutil cs resizeVolume lvUUID %100

4) Once it completes, exit terminal. Open up System Preferences > Startup Disk and re-select the volume to Bless it again as the boot volume.

I managed up to stage 3 but this command which went thru the motions ended with

$ sudo diskutil cs resizeVolume E585B180-07E5-4A4D-935E-DE4BC3B6DEC5 0g ...... [I did also try %100 with the same result]

The Core Storage Logical Volume UUID is E585B180-07E5-4A4D-935E-DE4BC3B6DEC5

Started CoreStorage operation

Verifying file system

Using live mode

Performing live verification

Checking Journaled HFS Plus volume

Checking extents overflow file

Checking catalog hierarchy

Checking extended attributes file

Checking volume information

The volume Partition 1 appears to be OK

File system check exit code is 0

Growing Logical Volume

Resizing Core Storage Logical Volume structures

Error: -69720: There is not enough free space in the Core Storage Logical Volume Group for this operation

so I am currently stuck

my hard disk lists as

+-- Logical Volume Group 20644543-688F-4880-80C4-1D10E179C95A

=========================================================

Name: Macintosh HD

Status: Online

Size: 508179988480 B (508.2 GB)

Free Space: 204800 B (204.8 KB)

|

+-< Physical Volume 79DD9B2F-B3F7-4224-80DC-C274BC565C61

| ----------------------------------------------------

| Index: 0

| Disk: disk0s2

| Status: Online

| Size: 120988852224 B (121.0 GB)

|

+-< Physical Volume D0CE3784-A4A0-4073-945D-8900475666E0

| ----------------------------------------------------

| Index: 1

| Disk: disk1s2

| Status: Online

| Size: 387191136256 B (387.2 GB)

|

+-> Logical Volume Family 13C2D605-87DA-45A7-81D9-9351F4969F4C

----------------------------------------------------------

Encryption Status: Unlocked

Encryption Type: None

Conversion Status: NoConversion

Conversion Direction: -none-

Has Encrypted Extents: No

Fully Secure: No

Passphrase Required: No

|

+-> Logical Volume E585B180-07E5-4A4D-935E-DE4BC3B6DEC5

---------------------------------------------------

Disk: disk2

Status: Online

Size (Total): 499672416256 B (499.7 GB)

Conversion Progress: -none-

Revertible: No

LV Name: Partition 1

Volume Name: Partition 1

Content Hint: Apple_HFS

but it doesn't show the Free Space 'partition' of 612 odd gb. (The hard disk is in fact nominally 1.2 tb.

So I do not know where to go next. I fear that if I just go ahead and ease the hard disk I will be left with a hard disk of just 500 gb.

Eventually I have found a solution for my problem

It appears that a fusion drive – a hard disk combined with a ssd –behaves differently and that least in Yosemite the disk utility does not handle the situation I got myself into; [creating a partition of the fusion hard disk and then trying to reorganise the partitions by deleting the newly created partition].

http://support.apple.com/en-gb/HT202574

The solution I found after trying a number of others is described at

http://forums.macrumors.com/threads/fusion-drive-partition-trouble.1519940/

There are a couple of suggestions here. One is resizing the CoreStorage which did not work for me, another involved bootcamp which I do not use. The final one essentially requires the deletion of the CoreStorage and then in recovery mode the disk utility will recognise that the hard disk and ssd require fixing and repair can take place. It is fully described.

I wish I wish I had known about this before.

I also wish someone might have responded to my original posting as it appears that it is not a totally unusual problem, it would have saved about 10 days of searching out a solution.